I won't lie. Finding yourself naked as a child, window closed...and being moved in a field? Get your anus checked...you alien love machine

(jk)
On a serious note, I myself have woken up while doing the wife. Apparently I got busy when I was sleeping away, she thought I was awake until about half way through I woke up and was like "Hell yeah, better than an alarm clock!". I've also woken up sitting on the edge of my bed, peeing, half naked and laughing, to name some. It's natural.
I've witnessed my brother in law, when he was a youngster (8 or so ) constantly sleep walking, talking to himself, changing his clothes, using the bathroom, drinking water and so on. We had to guide him back to bed so his big sis and I could...nevermind ;D
My oldest son gets up and wanders, he's 8 now and has been doing it for a couple of years. Like his uncle did.
Personally I think that the brain wakes up to a degree to allow basic motor function and control, and the subconcious takes control of the body. This is what allows higher functions such as sex, having a snack, drink of water, peeing, and so on. I don't think that you'd start the NY Times crossword puzzle with any success, but dressing/undressing, nookie, eating, all the basics you do while awake and don't think about it? Perfectly reasonable.