If you are crazy then so am I. I kind of have those fears but not as severe as yours. I am still sleeping on a waterbed - the kind that sits on a wooden frame so there is nowhere for anything or anyone to hide under the bed. I don't know if they sell those kind anymore but I am planning to get a "regular" bed soon so you can have my waterbed if you think that would help! Of course, I will have to start checking under my new bed.
As for closets, I don't necessarily check inside of my closet before I go to bed but the closet door has to be completely shut all of the way or else I can't sleep. It is as if I think that if something somehow got in there, it would stay in there and not bother me as long as that closet door is shut all of the way! Now who is crazier - you or I?!