I have a phobia about public speaking. Unfortunately (or maybe fortunately) my job required me to do lots of it. My body would go into flight or fight mode, it would be painful before and during. The reason is that the mind confused a threat to the ego (embarrassement, making mistakes, not being good enough etc.) with a threat to my life, and the feelings of discomfort kick in, and can be very powerful. It wasn't rational to react like that, but it is quite common.
In your case I don't know if it is irrational to be that uncomfortable, only you can decide. If you are depending on that money for food and to live, or if you are risking too much, or don't have an edge, then perhaps it is rational to fear losses and feel pain, and your body is telling you that.
But lets assume you are risking a small %, your life (and account) isn't at risk and you have an edge, then the reaction should not logically be there. Again, it is of course very common.
So then you have to try to short circuit this cycle and do something about the ego, and disconnect a thought process from a bodily reaction or feeling. The thought process is that you lost on a trade, but so what. You lost yesterday, or last year or whenever, so why is this loss making you feel uncomfortable and those past ones aren't. If you felt tense afterwards, pulse quickening, feeling of discomfort, adrenaline flowing more than normal or any other type of reaction, that doesn't need to be there. There are ways to disconnect it. I won't say it is easy or always achievable, but it has been beneficial to me.
Alcohol or drugs can do it, but please don't.
Cognitive behavioural therapy is the modern medical method.
Meditation has been around for millenia, works towards achieving it, and you can do it from anywhere, so that's what I use.
Also here is a post
http://www.trade2win.com/boards/general-trading-chat/88622-breaking-down-mental-illness-taboo-2.html#post1067752
That explains it in a better way than I can.