Invisible letters.
Like when you are going to bed but you think of a million things that you should do the next day. Like who you should call or detailed dialogue you might have with people you might see that day. Things that happened in your childhood that you flash upon or a phone number you want to look up, and perhaps call, or not. What you want to do with your life and how to sell stuff on e-bay to make extra money. How you are seriously going to reinvent yourself and improve your life as soon as you wake up. The only problem is that you haven't even gone to sleep yet.