Do you ever forget who you are?

I have a friend that recently forgot who she was, it was very random. She was missing for about 7 days and found riding a greyhound bus to Oakland California but she lives in Utah, it was very confusing for everyone, she was taken to the hospital and went into an unresponsive state for about 6 weeks then she snapped out of it. But has not memory of her experience. what could cause this all of her medical doctors are stumped