Very similar to all the "she was too drunk" replies, but she was a Type 1 diabetic. Great first date and we're at my place, naked, in my bed, and just after she said "I'm going to fuck you silly" while straddling me and making out, her personality changed as her blood sugar went ridiculously low and she sort of rolled off me and just lay there. I stopped and told her we weren't doing anything until she checked her blood sugar. Took a while as she was having trouble focusing on getting blood from her finger, but when I threatened to call an ambulance she finally got enough blood to get a result. She was very low (like 35?), so she desperately needed some juice, gummy bears, whatever.

Later I learned that if a diabetic is acting like that they're always low. I knew something was off, but wasn't sure if she was low or high. But yeah... if they're acting generally drunk they need sugar.

We got her blood sugar back to a comfortable level, I gave her a pair of shorts and a t-shirt, and she stayed the night and we just cuddled. We went to brunch the next morning, and that turned into one of my most significant relationships.