Sometimes (very rarely) i find my shirt or shorts removed when i wake up without memories of removing it.
Do you also wake up with a burning sensation in one or more body cavities? Do you live with someone? If you answer yes to both question, the answer might violate you!
sometimes I went downstair without me noticing or remembering doing it. My sister told me and she was too scared to talk to me since it was 3 am or something
You don't necessarily have to be sleep walking to remove your own clothes in your sleep. It's possible you're doing it while barely awake or just straight up while you're sleeping. Well, I wouldn't understand. I sleep naked after all.
I wouldn't consider it sleepwalking, no. It's closer to throwing your blanket or something, honestly, if you struggled out of your clothes. Getting out of bed, taking your clothes off, and putting them in the laundry hamper, on the other hand, would be sleepwalking. Except that I'd suggest your mom/wife/sister/neighbour/dog was stripping you. That, or you just don't remember doing it.
Sleep has cycles one prolly has like 4 stages of deep sleep every night, you undress between them and you don't remember. @Edit During deep sleep you're supposed to be paralyzed, and yet you wake up in different position than you went to sleep. Coincidence? I think not.
Honestly if your alone, its very hard to notice. Maybe if you messed up Ur room while u were walking XD. I used live with someone having a sleep walking sickness, and it's scary at first, then just becomes a habit. Edit - now I remember it, there was another person who used to sleep talk, well mostly swear "f@#k u, b@##h....."