I have a lot of de-personalization episodes (which, in case you don't know, is basically feeling like nothing is real, everything is a movie or something...) as well as having some de-realization (something that kind of makes you feel entirely separate from everything else). Because of that, I often can't trust myself. I have a friend who is really awesome. For some reason I never feel that he isn't real, or part of this unreality, or the outside world, or whatever. Whenever I begin experiencing the sense of unreality, I call him and ask him questions (like - 'did I really see suchandsuch today?' 'Did thisandthis happen?')
Perhaps trying to find someone you can trust like that would be beneficial.

I haven't had much success in having people not think I'm crazy. My mom is still too weirded out to talk about my disorder. The rest of my family doesn't know my diagnosis. My one friend (who I mentioned above) knows... that's about it (other than my doctors, of course). There is still a lot of mystification about bipolar and many other mental illnesses. I think the best course of action would be to explain the disorder to the person as fully as you can. If it is your doc, then just work on building trust. Most docs have seen a lot from other patients and wont be as flippant about you as someone who doesn't understand the disorder.