Originally Posted by
1989Pre
Any great stress will lead to (temporary or permanent) over-stimulation of the adrenals "fight-or-flight response". Hi246's commentary is valid, but I think the endocrine system is also involved. Nature has adapted us to not need to eat, drink and digest when any level of threat is perceived.
This was my thought too. It has manifested itself most often on high intensity days like crits or VO2max workouts, but long hard days would trigger it too. Gotta stay light when you're running gazelles into exhaustion on the savanna.