On some tours I have gone up and down mountain passes or steep hills all day without too much trouble. But two consecutive all-day climbs in the Alps nearly did me in. I was unable to deliver power to my legs for about five days afterwards, which meant that I spent a big chunk of that holiday holed up in a hotel room.
In hindsight, I can see that I should have noticed the problem developing. But if there is a lesson that others can learn from, it is to let your body be your guide. If doing something hurts, or you find yourself hitting wall after wall, then it's time to take a break, stop, and find another way.
There is a big difference between all-day ascending and all-day ascending AND descending. Obviously, the latter is gentler on the body because your muscles have more time to recover.