This actually made me think of something that's been happening to me lately. I've always had what's called hypnogogic hallucinations, basically dreams outside of the REM phase. (I also get sleep paralysis, lucky me!) But lately as I wake up from these (so it's like I'm dozing, in a light stage of sleep, then I kind of wake up) I have the quickly receding memory of something I just dreamt, only its seems like it's important, but I can't quite remember what it was. It's more like I know I knew something, but cannot remember what it was. Just that it was important. I wish I could describe it better. But it's the strangest thing.