Why did I wet the bed last night?

I'm a 15 year old female and this has NEVER happened before since I was a little kid. And I did drink water before I went to bed, but I usually wake up when I do need to use the restroom :/ so i dreamed about using the restroom, but I didn't wake up cause I was in the middle of REM stage. And I'm on my period too so that's even more embarrassing D: