I masturbated in my sleep. no, really..

About two years ago, one night I was dreaming. I do not recall exactly what the dream was but I can safely say it had something to do with sex. While I was dreaming, I remember having this awesome time and feeling so good. I woke up suddenly and saw I was holding my penis in my hand and my clothes covered in sperm. I sat there for about a minute, a bit freaked out by what the hell just happened. During the whole -process- I was completely asleep, in dreamland, having a sexy time.
This kinda reminds me of sleepwalking (sleepwanking?) but I was never a sleepwalker. Has anyone else done this before, Is it normal?