Mom?

I haven't been feeling too well the last few days and with sick kids, I have been drained. Today I decided to take a quick nap in the bedroom while my husband and the kids hung out downstairs. I don't remember what had woke me, but I was laying in bed awake with my eyes closed. As clear as day, from within the room I was in, I heard someone say, "mom". I looked up expecting to see my daughter standing in the doorway. No one. The door was still closed. I sleep with a fan on to drown out background noise so in order for me to hear a voice that clearly with my door closed, it would have to have been coming from within the room with me or from right outside the door. I immediately got up and opened the door to find that I was alone upstairs. Upon going downstairs, my husband confirmed that no one had been up there and that no one had called for me.