Re: Man, what's up with my heart?..

 You sound like you are very sympathetic dominant.  (we all are).  You are kicking out adrenaline at the slightest provocation.

Have you been doing any meditation? The book the relaxation response is also very helpful. Describes a specific way to meditate.

http://www.amazon.com/exec/obidos/tg/detail/-/0380006766/qid=1034031878/sr=8-...

Here is a summary

http://www.relaxationresponse.org/steps/

I've been able to calm my startle response.  We have a cat that tests it for me all the time.  She sneaks up behind me, jumps up on the table and meows as she lands right beside me.  This used to make me act like a startled baby.....complete with my hands shaking in front of me.  Now I barely get startled.

Good luck !