I have had two separate incidents where after a ride that was significantly longer than my typical rides I developed flu-like symptoms (head ache, nausea, chills, and weakness).
Both times the workout felt unusually good and I was able to ride without issue throughout, but around 6 hours after the ride, I started to feel pretty terrible. The symptoms continued to a lesser degree the next morning (in both cases I rested the next day), but were gone by the next afternoon/evening.
My googling of these symptoms seemed to indicate overtraining, but I didn't have any lingering effects and I hadn't increased my workout routine by more than 10%. Only the individual rides were longer than usual.
Has anyone had a similar experience? If so, what should I do to prevent it in the future? Is it possible to develop short-term symptoms of overtraining from a single workout?