Oh my God, you have NO IDEA how happy I am to know that I'm not the only one this has happened to!
I'm a writer, and I find that this often happens to me when I'm working. I've also done it a few times during chatting as well. Sometimes what I end up typing is coherent, but just last night, in the middle of a chapter I was writing, I typed this:
"I don't intend to be alone with precious nipple."
... yeeeeah. I have no idea.
Other sleep disorders run in my family- sleepwalking/talking, and I have semi-frequent bouts of sleep paralysis. I wonder if this is related...
Thank you for posting this. When I googled 'sleep typing' I was so afraid I would come up with nothing!