wet bed

This may be TMI, but bear with me.
Last night, I was up late watching Sex and the City in the living room when I heard Chris scream from the bedroom. At first I didn't think I was him. I thought it was someone outside because it was kind of muted. But then I heard more talking and then he walked out into the living room. He looked so confused. I switched into maternal mode and went in the bedroom to see what happened. There was this huge wet spot on the bed and on his pillow. It was soaked down to the mattress. We stripped the bed, dried the mattress and put clean sheets on the bed. The reason I am sharing this is because we have no idea how on earth this happened. It was so crazy. We started ruling things out. Definitely not pee. Totally wrong place for that to be it. It was not hot in the room, so it couldn't be sweat. Plus, even when it's 120 he does not soak the bed like that. Plus, and this is kinda gross but it's reality, it didn't smell like sweat. He had taken a shower before he went to bed, but he was dry when he got in bed. So, that wasn't it either. We kept looking around thinking if something had fallen from somewhere, but there was nothing. There was nothing on the headboard that could have caused that wetness and there was no spot on the ceiling. We couldn't figure it out. Did he puke water? He said he didn't think so. Plus that didn't smell like that either. It didn't smell at all. Meaning it was just regular water. It couldn't have come in from the window. Not only are we on the second floor, but his side of the bed is no where near the open window. How did this happen? This is crazy. We still cannot figure it out. It's the strangest thing.