Owning up to it.
Know you have made a mistake and it is a fact. Stop blaming anything or anyone else. Owning up to a mistake is the start. The sooner that you realize that mistakes can be made and will be made, then the sooner will you get back into the game.
Learn from it.
Now what went wrong? Got it? Good. Every mistake is a learning experience. Even if the reason you realized is your own arrogance, greed, or some flaw in your calculations or in your strategy, there is something to learn. At least you know what not to do next time. The forex market is not as unforgiving as you might think. It is a place of chance and opportunity.
Try a new path.
Now you know the flaw in your strategy, reassess if you would change that part alone or totally try a new path. Failure gives us the chance to look at our plan from afar, to give us a bigger picture. If the problem seems to be your fear of losing or a system that does not fit you, you can easily see a better and new approach once you open your mind to them.
Assess the effects of the mistake.
What are the changes from your previous situation? You may find that you are not that worse off after all. You might be overacting a bit about the situation. However, if the mistake really has far-reaching effects, then better to list them. This way, you can asses which effects can be remedied and which you can do nothing about. For example, you may have lost some investment, but if you can see chance of recovering it, you will discover if it is feasible or not by listing the pros and cons.
Perhaps you lacked discipline before. Then now is the best chance to wake up and make a solid system where you will base all your decisions. Learn the tell tale signs of the errors you have made so you can avoid them. Not only will a systematic approach make you more confident in making trades, but also lessen the work you normally do.
I know it is easier to say, but really best thing to do is be stubborn and get back in the game. They do not call forex trading the perfect marketplace for nothing. If there is currency dropping somewhere, then there must be a rise somewhere too. There is always a chance for profit. Think that if your tread the balance of taking the right risks and being conservative at the right time, then success is not too far.
As a last thought, think about the fact that you are not alone. Somebody else somewhere has made a mistake before you. In fact, those who have tripped are probably the ones enjoying success now. They have learned their lessons from failure. They have shrugged off the stigma of a loss based on just one fatal mistake. Forex trading is difficult and challenging yes, but you are always welcome to try again and again.