There is no doubt that the ego of most men takes a real bruising over this. I can certainly say it was/is true for me, it screwed with my head in the extreme and made a lot of days and nights quite miserable. I don't think our partners really often understand how troubling this is to us, that it's not just an 'in-the-moment' experience, but something that preoccupies us and pervades our days (part of the problem). Our ideas of manhood get all wrapped up in there and just make the problem worse, no doubt.
Here are a couple of great articles that I've shared with my partner that were helpful for her to understand:
Honestly the audio programs above, especially the hypnosis one, are really very helpful. They describe a bit about how anxiety and fear work, and how they are designed for fight or flight. In fear our body shuts down all kinds of systems, hormone production, digestion, sexual function, etc. This is because in a fight or flight situation we don't need to eat or f*ck or whatever (this is why we can get dry mouth in moments of shock/fear, digestion is being turned off). These responses are shut down to provide the maximum amount of available energy for the danger that we need to respond to (hungry lion approaching). But when we use our imagination to create fear and anxiety around a situation that's not actually threatening, or should be pleasurable, we start to create an unhealthy relationship to a situation which need not cause fear/anxiety. And it goes on through a couple of visualization exercises, etc.
For me it really has been about relaxing and coming back to a pleasure centric focus. I still struggle with the anxiety part, the preoccupation with an upcoming event not in the present i.e. date night, knowing we have intimate time planned etc. But I've been really grateful to have begun letting go of the in-the-moment fear at the time of the event. I think part of the road for me has been accepting that it's ok to experience the anxiety during the day. That I don't need to dwell on it, but that it doesn't necessarily have to 'mean something' if I have some flashes of it.
I still have needed a little extra help getting going in the bedroom from time to time, but once I'm in pleasure mode things seem to be going much more smoothly! But I have to continue to remember that I tend to be an obsessive person and that if I start allowing myself to have a mentally unhealthy relationship to thoughts of sex in my head that this problem can return, but that it need not be a problem if I continue to cultivate a more healthy attitude in relationship to my thoughts and feelings about sex.