OK just generally, everything that happens to you is stored in your muscles and organs, so all of this stress builds up as knots in your muscles, etc.
When you begin meditating your are working at relaxing all of your muscles, so these various stresses will begin to work out. I'm at the point now where I can feel these stress knots forming and then run some energy into that point to help relax it. However, that energy (stress) in the muscle still has to go somewhere, so that it can be released from your system.
That's why you'll occasionally find yourself bursting into tears or laughter and not understanding why. It's just stuff that has to be released.
As you get more into meditation you'll find that you don't store as much stress in your system as you used to, and you'll find that it's easier to releases the stresses that you do store.
Yoga is also a massive help with this as the stretching and breathing helps clean you out also.
Hope that helps,
Robert Morgen www.highmountainhoshin.com