There was a skit on SNL years ago (Kevin Nealon, I think), where he was an adult film reviewer. I don't remember it well, but his reviews went something like this:
This week I watched Debbie Does Dallas. At first I was interested....interested....interested....more interested....VERY interested....not interested
This would repeat for any of the movies he reviewed. A funny metaphor about a man's phases of arousal.
Don't worry, I think that it's universal that all of those hot ideas you have when you're really horny just don't sound hot, and maybe even shameful, when you reach the "not interested" phase.
Also, I've heard that men actually do have a little period of depression after orgasm. So that would play right into feeling negative about what turned you on before. Of course, after that wears off and the hormones kick back in, it's game-on all over again.