You're dealing with empathy. It's not insane, it's not you going crazy, it's not some psychological disorder, you're not being delusional. A good place to go for thoroughly-researched information on empathy is the
Universal Empath Report. A sort of "empathy 101" site and collection of essays. Read through that, first of all; it should help a bit.
"Is it possible to learn to shut people out?"
Yes, it's called shielding. Call it a visualization, mind over matter, whatever you wish, if you're not comfortable with more new-age-ish concepts and ideas. Perhaps it's energy manipulation, perhaps it's meditation or concentration on something other than emotion that shuts outside emotion out, but it works for a lot of people. Visualize a wall, bubble, sphere, whichever, all around you - above, below, around. Whatever visualization works for you. Build it piece by piece, brick by brick, or start it as a small bubble or egg in the palm of your hand that grows and grows till it surrounds you, keeping out everyone and everything else, containing you.
Some people visualize an egg, some a wall, some a bubble, some a globe of white light. For instance, A friend of mine has a highly sensitive 8-year-old daughter who gets easily overwhelmed when around too many people or too much emotion - one time, at a funeral of a person she didn't even know, she started crying and couldn't stop, almost seeming to have a sort of panic attack, because she was being so influenced by so many peoples' emotions. She didn't like the egg visualization, so my friend asked her what she thought would work. So her daughter visualized a banana peel around her, complete
with stem. If it works, use it!
I myself tend to visualize a globe of silver fire when I need to throw up a quick shield, or a thorough layered web overtop obsidian rock when I know I'm going into an emotionally charged situation and need strong impenetrable shields. I, however, hate shielding and do it only when others' emotions get to be overwhelming, to the point where I feel like I'm going to panic or break down. Why? Because it feels like muting a vital sense, like putting cotton in my ears or having gauze over my eyes, or wearing gloves. I rely on my empathic sense more than I usually realize, when dealing with or reacting to people.
"Can a loss of a person or something similar heighten a person's sensitivity? Is it permanent?"
Highly emotional occurances, often to the level of emotional trauma, tend to have an effect on one's psyche, and that often extends to sensitivity. It can dull it, heighten it, shut it off altogether, or blow open previously inactive abilities, depending on the person and the event. It can be permanent, but not always, from what I understand.
"I also feel like I am invading people's privacy. Can I learn to do this selectively? Is this really that unusual? Sometimes it is so strong that it almost feels like telepathy (although it is not). I can't always put a name to the emotions I get from others -- I just FEEL them, which makes it worse."
Yes, you can do this selectively. Shield constantly, and just drop shields or send out "feelers" (reach out mentally to probe someone's thoughts/emotions/sense) when you want to feel someone out, feel someone's emotions. It's not incredibly unusual; I know a fair amount of people with varying degrees of empathy, whether they call it that or not. Strong empathy, overwhelmingly strong, is a bit more unusual, but not insanely rare. I understand not being able to put a name to incoming emotions or feelings, though; I have the same problem at times as well.
"I still find it hard to believe that everyone can't do this, thateveryone doesn't have this ability. I have felt this for so long(although lately, as I mentioned, it has gotten more intense), that I always thought that this was just a normal thing."
A lot of people I know believe that everyone's empathic to some level - only sociopaths have absolutely no empathy, or completely blocked-off empathy. However, some people have stronger empathic sensitivity than others, and some people shut it off or block it off early on. You can imagine that some people just can't deal with it, and so they do a sort of dissociation.
"What do the rest of you do? I mean, when you have strong feelingsfrom another person who needs you, and you need to share it with another, but you are afraid of how they will react to what you say?"
I have a couple pagan friends I can talk to. People who aren't involved with mystical stuff, new-age type stuff, etc tend not to believe such things or be at all knowledgable about such things. I was accepting of my empathy and a couple other odd things before I ever converted (that the right word for the situation?) to paganism; I was christian before.
"Is there a way of SENDING, not just receiving, for those of us who have this...ability?"
Yes, it's called empathic projection, but not everyone can do it, and the person you're projecting to has to be aware of things or conscious of stuff to receive it (or realize what they're receiving beyond mistaking it for their own feelings). I believe someone else already touched on this in reply to your posts.
The best way I've found to deal with empathy - the only way, besides blocking it all off with constant shielding - is to know yourself, your emotions, the way you react to things. And to be aware of yourself and your own emotions, at all times. That way, if you start feeling someone else's emotions, you can recognize that it's not *your* emotion, and you can deal with it accordingly. Oftentimes, when I start feeling any strong emotion, I stop and think "Why do I feel this way? What situation or thought caused this?" and if I can't think of a reason for the emotion, then I start looking around me to see who else seems to be feeling it. If no one in the area seems to be feeling that emotion, then I pick up the phone and call the people I have strong connections to (my best friend, my boyfriend, and a teacher of sorts of mine) in order to see if they're feeling that.
Differentiation between yourself and others is probably the most important part of dealing with empathic sensitivity, in my opinion.
Now, before I talk about psychometry or your issue with being connected with the one person you spoke with, I'm going to have to talk about something a little esoteric. If this strikes you as too new-age or too pagan or too damn insane to stomach, then just take it as a way of thinking about things or a way of visualizing. You've had psychological schooling; you've probably learned the power the mind has over the rest of the body/psyche/emotions/etc. So chalk the following up to that if it's too much to believe straight away.
Everything has energy. This is a law of physics. Anything you do, whether it be talking, moving, whichever, expends energy. This energy has to go somewhere; it's often taken in by other objects, the air, whichever. You jog for a while, you expend energy, you feel heated, the air around you heats a bit by taking in the energy you expend - it all works out. Logical so far?
Let's take it a step further, to the realm of emotion and the metaphysical. When you chat with another person, you expend energy, and when they listen to you chat, they take in that energy. It's an exchange of energy. You can consciously manipulate energy to certain ends, and this is what some people call "magic" - simple manipulations of existing energy. But that's getting a little too esoteric, most likely, so I'll move on.
Any energy exchange creates a link between the one who gave off the energy and the one who received it. This is evidenced in friendships, love relationships, and other types of relationships. The more time and effort and energy you put into any sort of relationship, the stronger it grows, and the stronger the connection between the two individuals becomes, forming a link, or even a strong bond in some cases. Sometimes energy impulses in whatever form (emotions, thoughts, impulses, etc) can pulse across this link, sent consciously or unconsciously.
Now we come to your connection. It sounds like you've formed a pretty strong connection with this other person, a fairly intense link through which emotion pulses strongly and regularly. As a bond, it can be cut, if need be. If you do not wish to have a link anymore, you can chop it off, but the stronger it is, the more painful and traumatic that severing is, and it takes a bit of esoteric knowledge. I don't recommend it; when I had a link severed with an ex-boyfriend of mine, I was shaking and crying for ten minutes afterwards, and I thought I'd been over the man.
A different way to end a link, less painful but much more slow, is to stop thinking of the other person. Don't contact them, don't receive anything from them, shield the link, and without maintenance, the link should eventually fade. How long it'll take I don't know, and it can be very easily rebuilt, so it's an iffy way of doing things.
If you wish to keep the link, however, as you seem to want, but want a way to deal with the amount and intensity of emotion coming through it, then you can just shield the link. I mentioned general shielding before, but those shields usually don't automatically shut out links. You have to shield those separately or consciously, and if you have a very strong link to someone, stuff's going to leak through no matter what. Use whatever visualization works for you, as before; I usually think of it as doors shutting, screen doors if I just want to mute things, or heavy safe doors if I want to shut as much out as possible.
Now, as for psychometry, the sensing of emotional residue from objects or places. I talked briefly about energy before. All energy has a flavor or a form - look at fire, electricity, wind, friction; they're all energy, just taking different forms. Energy can be flavored or charged with emotion, and that can saturate an object or area. Visit the sanctuary of a very old church sometime; you'll notice it. Or a funeral home, or a graveyard. Any place where there's frequent amounts of strong emotion or a specific emotion will have the feel of it. The knife a depressed adolescent used mostly just for self-cutting will have a certain feel to it; an engagement ring exchanged between two people who genuinely, strongly love each other will have a completely different feel. And so on and so forth. Oftentimes you can pick up on that emotion, sometimes get an idea of what the object was used for or how or where or why, just by probing and concentrating much as you would in trying to pick up emotions off of someone.
I hope that helps!
"Feeling it this strongly and this... focused?... actually feels physically odd and quite literally electric (<--- anyone else get that feeling? Is it normal?)."
For me, energy translates to a near-electric tingling on my skin or just under skin. The two very strong links I have with my closest companions feel as if they connect at my chest, so something coming through those links often feel like pressure in my chest, a tingling outward from the heart area, that sort of thing. Lesser links connect through arms, head, etc, and the tingling reacts accordingly in those areas. Others I've talked to sometimes experience tingling or reception of emotion as electric, static, warmth, etc, so it's fairly normal as far as I know.
"I need more practice, but I want to do this gradually, because I'm afraid of accidentally cutting it off, rather than just temporarily blocking it out."
Don't worry too much about that; from what I understand, a link as strong as the one you've described can't be cut off without great conscious difficulty, often needing the focus of ritual.
"When other people put walls up, I feel as if I have lost a sense, and it is very disorienting, like seeing someone's lips moving but not being able to hear them speak. I don't much care for that feeling."
I know the feeling! It's why I avoid shielding unless I have to. It's like losing a valuable sense and is very off-setting.