Drunk on fresh air?

I went for a ride today outside for the first time (wow!) and although I really took it easy (supposed to run 32km tomorrow morning) and thought I had enough sleep last night, I fell asleep during the middle of the day (pretty rare for me). Sure, the turbulent energy cascades I was studying at the time were extremely exciting, but I normally nod off just briefly...not for over two hours!!

I spoke with the guy I rode with and he fell asleep today as well. Did we really get drunk off of air that was just too fresh? Is it possible that my body was siphoning energy from re-circulated interior air all winter? Was my body just so excited to finally be in a wilderness setting and went so metabolically nuts that it tuckered me right out?

If so, it's going to be a sleepy summer!