I would say it is important to keep a certain amount of distance from the process. E.g. don't spend all your lunches in the lunchroom discussing how terrible everything is. Of course, this is a fine line to walk, because a certain amount of commiseration is very helpful, not to mention it is useful to stay in the loop. But there's an enormous relief in talking to friends in an entirely different world, doing some kind of athletic activity (or so I've heard), going to a movie, etc. 

One reasonable way of getting commiseration without the attendant misery is talking to people several years past your particular crisis -- close enough to remember the relevant details, but with enough perspective to screen out a certain amount of noise. Cultivate older friends, and also go out of your way to talk to younger people in transition.

I think that part of what is so daunting in these situations is their total uncertainty. Very important things are happening in your life on which your future depends, and you may or may not be able to affect them. Of course it is a lot to deal with. Especially as you are probably doing much of this for the first time, as in the cases you describe, so everything requires a great deal of thought and emotional energy.

It can help a lot to find a mentor and to find a support group ("in life a person is obligated to do two things for himself: to find a teacher, and to choose a friend"). The support group, as Ellen suggests, need not have anything to do with the actual process. Figure out what gives you perspective and make space in your life for this, ruthlessly if necessary. Many great people ended up making contributions in ways that they would not initially have imagined. You need to be very clear about your goals but also open enough to the possibilities of the world that you allow yourself to be surprised by unexpected opportunities. You can't do this if your every minute is spent stressing about the worry at hand.

The mentor or mentors should be people you trust and admire who have done this before and can give you advice and perspective. Think back to a major transition you went through -- applying to college for instance. What if you, as you are now, could talk to your previous self in the midst of that process? What things you would have to say! But if you choose your mentor wisely then s/he can tell you some of these now which can very much help you. And as Ellen suggests, you might also look up a high school student of your acquaintance and take them out for coffee.