Mommy thought that surely, this wouldn't happen to me because of how much hair I had when I was really little (and that at first I didn't lay on my back a lot because I was being held all of the time). But, sure enough, over the past month I have lost a lot of hair in a funny ring around my head. It's still long in the back and thinning out a bit on the top, but you can clearly see the ring. Mommy calls it my 'Monk's Mullet' and Daddy just prefers to keep a hat on me.
Don't worry, it will grow back!