My mother experienced the exact same issue while I was attending college. It was preceded by an intense migraine the night before (including vomiting). She call

My mother experienced the exact same issue while I was attending college. It was preceded by an intense migraine the night before (including vomiting). She called me early that morning very confused why she wasn't at school (she was a teacher). She didn't remember the night before, or why she had stayed home, or where my dad was (he had left for work). I was seriously alarmed, but she had no other impairments other than her memory. She was lucid, had clear speech, etc. I eventually pieced everything together (my dad is a doctor and he diagnosed her over the phone). I then spent the rest of the day on the phone with her, answering the same cycle of questions. I eventually had her start writing those questions and answers down, but she kept losing the paper! Eventually we moved it to the fridge, and a close friend of hers was with her. Similarly, it lasted about 24 hours, eventually faded, and had no adverse after effects. It truly was like Memento, though. Definitely one of the more surreal medical issues I've been exposed to.