I have a very unusually strange question.....

So this happened this morning......y husband and I woke up and saw on our sons carpet a big wet spot. We smelled it and it smells like pee. Dogs don't go upstairs at night and his door is closed tight so nothing gets in. He's 2. His pjs were still on and his diaper was on perfectly. There's no way he could take off his pjs and diaper and pee and get them back on perfectly with snaps??? No way. We looked around and there's nothing. No leaks, no water, no sippy cups...nothing!! We cannot figure out where this big wet pee came from. It wasn't there when he went to bed and this morning it was there. Any ideas??? I'm so freaked out and confused at this mystery.