1. Let's say you sit inside 3 hours watching TV. Now you do the same, sit outside and read a book in the breeze, and you get much sleepier/tired. Why? I assume it has something to do with more oxygen in the air. In a closed environment the breathed out air sooner or later fills up the room, and less oxygen enters the brain, slowing the body down. At least that is my theory. 2 Well, since we are at it, why in the winter one gets more tired than let's say in the spring? 1 hour of dogwalking in the cold makes me way more sleepy, than doing the same in warm weather. Here my theory says that in the cold the body has to work extra to warm up the air before it reaches the lung, thus more energy is used for the same activity. Is that right?