Ahh, now that's different. I'll leave the questions of logistics in the whole IMing-yourself thing for later, as I can think of a few ways to do it, but very few that can be done unknowingly.

In Secret Window, the main character is a switch but doesn't know it. He's kind of a hollywood switch in that his alter is a violent form of himself that he subconsciously created to deal with things he couldn't do himself, but the way a lot of that is executed strikes pretty close to true...actually pretty accurate to textbook DID, if not healthy multiplicity. You should totally see it if you like dark movies with odd twists that don't fit into the mold, and Johnny Depp is amazing in it, too <3

-Dan