If you've been reading a lot that day, the mind can get in hyper word recognition mode, so that when you rest your eyes you still see letters jumping around. It's a lot like getting a song stuck in your head. That part is normal.
I have no idea why you make scary sentences out of them. Maybe the words popping up are freaking you out so much that you're worried you're going crazy, and start to imagine that they're spelling out crazy things. My bet is that if you don't panic next time this happens, you won't see any messages. If you still do, it's probably not crazy-crazy, but there might be something wrong that your thoughts always go negative. Probably an anxiety disorder. See a therapist.
I have no idea why you make scary sentences out of them. Maybe the words popping up are freaking you out so much that you're worried you're going crazy, and start to imagine that they're spelling out crazy things. My bet is that if you don't panic next time this happens, you won't see any messages. If you still do, it's probably not crazy-crazy, but there might be something wrong that your thoughts always go negative. Probably an anxiety disorder. See a therapist.