SUBREDDIT: r/relationships
TITLE: I [21M] may have discovered a whole new side to my girlfriend [22F] of 3 years. I'm a little scared.
POST: Hi, so my girlfriend an I have been dating for a whole now and have always enjoyed a very active and slightly kinky sex life. Nothing too hardcore but we enjoy experimenting with different positions and light role play. Anyways, my birthday is coming up and she bought this tiny anime-style schoolgirl outfit as a treat for me because she knows I'm into that. It arrived in the mail yesterday and we decided to "test drive" it today. She put it on and right away we knew this was great for the both of us. We were having fun and after round 2 she told me to lie on my back. She got on top and had this look in her eyes that I had NEVER seen in 3 years of dating her. She said "I'll destroy you" and right after she started clawing an biting at me a lot more than she usually does. Then she asked me to pull her hair and smack her butt which was all good and fine, but just the way she said it, it was almost feral. When we were done and we were both laying there in bed cuddling, I said "that was new, you're gonna destroy me, huh?" And she said "what are you talking about?" I thought she was playing with me, but she seriously did not remember any of our third round of sex. Between the whole "ill destroy you", the fierce look in her eyes, the slightly uncharacteristic S&M, and the fact that she doesn't remember ANY of it... I'm honestly a little scared that she might have multiple personalities. I know she has a history of mental health issues. But it always just depression. Although I could see how a more violent personality could develop from depression. I don't know. I honestly a little scared. I love this girl, but I don't know if I can love that part of her, if it really is another part of her. It was too fierce for me, I was scared.
TL;DR: 
girlfriend said "I will destroy you" during sex and got very fierce and S&M on me, but recalls none of it. I'm scared it's a split personality of hers. Help?