In my years I've been a keen swimmer and cyclist. When I'm pool swimming, I don't usually get that euphoric high until the cool air of outside hits me in the fa

In my years I've been a keen swimmer and cyclist. When I'm pool swimming, I don't usually get that euphoric high until the cool air of outside hits me in the face as I'm leaving the building. The harder I swam, the higher the high, but it never hits me until the outside air hits my lungs. It's incomparable. When I'm on my bike, I reach that same meditative trance. It's just the road, the pain in my legs and lungs and the focus on getting to the end of my ride, little by little, kilometre by kilometre. Everything else just falls away. My problems don't matter when I'm on my bike. The pain ensures that my focus is occupied and I'm present. Completely present. When I reach the end of my ride and fall from my bike because my legs won't carry me, the high comes as I lay trying to catch my breath. There may be something to your observation that it could be related to hypoxia. Either way, the high is real.