Yeah, let him/her know, but if it was me, I wouldn't make a special appointment for it. I had something like this happen to me when I was about 14 or 15. From where my bed was positioned at the time, I could see all the way down the hall into the living room where my dad had left a lava lamp on. I was drifting off to sleep when suddenly I thought I saw the lava lamp catch our curtains on fire since it was setting close to a pair of them. I tried to scream to my dad that our house was catching on fire, but I couldn't scream. I just laid there watching it for a little bit because there was nothing else I could do. Finally I 'woke up' and realized that everything was fine. It was still really unsettling though. I guess it is possible for the brain to fall asleep and dream even if your eyes are still open.