Skeptical of my fantasies when I come

I consider myself to be quite kinky, I've never had sex before so I've not tried anything out. Anyway, when I'm masturbating I fantasise about situations but when I reach climax and come, I'm all of a sudden skeptical of whether I want what I fantasised about. And it even happens for some vanilla situations. If anyone has been through this I need to know. Does this go away when I first have sex? If it doesn't, how do I live with the regret I have after I have sex?