Reading through the thread it seems like the majority go with 'you have emotions, they are unavoidable, you have to learn to cope with them.' etc etc. This imo is a bad approach.
As ive said before,imo and experience, you cant feel anything unless you think it first. It follows then that you should be very careful of what and how you think, and in turn, believe. Because just like a person suffering from depression, if your thoughts / beliefs are distorted from reality (in a way that detrimental to you) youre in for one rough irrational ride.
Physical:
About the only physical way trading can negatively affect you (outside of you stressing yourself silly) imo is the loss of money, so you have to be realistic about what losing X amount of money means to you. Its called 'risk capital' for a reason, its at real risk! In part from the market, but mainly from you becoming emotionally destabilized, and being a wally. Only trade with money you can afford (mentally and physically) to lose.
Mental:
The ways in which we can mentally mess ourselves up is endless. The one thing they will all have in common, be they thoughts / beliefs / expectations, whatever, is that they will all be unrealistic next to reality. You have to find out which parts are relevant to you, which personally cause you distress and compare them with reality as best you can. From there things become easier as its really difficult to believe something that is obviously untrue.
How can you change the way you think / what you you believe etc? Buy a decent book on CBT / depression, grab a pen and paper and get busy. "Nah! That psychobabble aint for me!"... Well done genius, youve just unwittingly defeated yourself.
Imo and experience, when you get this stuff lined up, trading can be pretty stressless.
As suggested earlier, when youre under your own personal gun, measure your heartbeat and compare to 'at rest'. Do the same again when youve done some work on yourself mentally.