To quote excerpts from Jim Cramer's article back in 2000 (Jim is the hothead himself on CNBC)
"During those periods it is vital to retreat from the battlefield, where the casualties incur such a sting that they can affect your judgment in a negative way. As we are both extremely affected by the emotions of both losing money and losing in the face of competition, it is important to recall that we always succeed when we approach the process with teamwork and without emotion. We always prolong the agony when we are down on each other or down on ourselves. The fortunes of the firm depend on us, not the market, as we have shown an ability to make money, regardless of the market's direction."
"At all times the propensity to be angry or second-guess will color much of your thinking. You must consciously go beyond that. You will no doubt, in the course of the battle, replay and even undo certain trades that would have turned out to be good trades. These are casualties of war and every great army suffers them. If you dwell on them you will miss that opening in the enemy's flank that was meant for you to turn the battle around."
I especially LOVE this paragraph, talking about reserves (reserve=capital):
"The possibility exists that you may be doing too much at one level. Given the fallibility of any human being's thought processes, this instinct is most likely correct. Even when you think there is an opening to play offensively, you must guard against committing a reserve until you feel it is right. Great generals commit reserves when they don't need them, to be sure they crush the enemy. Bad generals commit reserves because they have planned poorly and are out of options."
What do I do when I lose my nerve? I look at the statements above, I review my basic trading rules, then get away. Go do something else. The market will always be there.