Also you can do therapy yourself, you don't need a specialist - everything you need to do is be honest about what you're going through and aware of your feelings. Once you've managed to pin-point what it is that you are feeling (anger, despair, frustration), determine what the cause is (showdown lost at river, higher flush, etc) and then rationalize it (finding an explanation, such as the fact that it can happen to anyone).
Going through this process will take off the edge, but also make you feel more in touch with yourself, thus, more in control of your actions. Being in control is a key factor when playing poker - winning or loosing happens either way.