Doing anything
properly IMHO is tiring as it proves that you are concentrating 100%
I worry about people who step out of a car after a 500 mile car journey feeling fresh as a daisy,I always feel knackered.I seem to spend the whole journey weighing up others,trying to predict what they might do etc ( born out of trying to survive on a motorbike) and find it quite draining.
I suspect the super relaxed types could possibly going on 'mental autopilot'.
Safe flying
MM