video about this at the NYT today. I read the book Sybil in high school and found it fascinating. Come to find out, there's been some debunking of the MPD diagnosis. That's one reason it's been renamed. Instead of more than one personality, people with DID have less than one personality. Their personalities are fragmented and they have trouble integrating these fragments into one cohesive whole.
I don't think I have DID and I highly doubt that you have it. Long story short: It's extremely rare and some doctors don't even believe it exists, so if you're worrying about having DID, just let it go. You're probably fine.