Question about dreams.

Well, I just have a couple of questions about dreams. I've realized that when I wake up the next day, unless it was a very interesting or funny dream I can't remember it no matter what. But when I have a weird, crazy, or just normal dream, the only time I can remember it is if I lay down with my eyes close, but as soon as I sit up or stand up, I can't remember it. As long as I lay down and close my eyes, I can, but all day if I don't lay down with eyes close, I can't remember. I can be up all day, but as soon as I lay down and close my eyes to rest them for a few minutes, I remember it like nothing. I was just wondering, does this happen to anyone else? or Why it does that? Or what it could be? Thanks for your help and time.