My 11 year old son started complaining of headaches soon after the school year started. I noticed that sometimes, he would come home from school and lay down for awhile. But when it became apparent that was having headaches in the afternoon, more often than not, I knew something wasn’t right. After questioning him, I discovered the headaches would start just a couple of hours into the school day. That’s when I realized it was the mask, which makes since, because you’re not getting as much O2 to the brain, even though probably a very small amount, over time it makes a difference.