No real answer...

...But I'm going to pose the question anyway:
When do you push through physical/muscle tiredness to do something *correctly* and when do you just call it quits for the day?

Bonus question: How is it possible that by not riding for only *3 days* I can lose enough muscle tone/body awareness such that my position degrades as as much as was demonstrated at tonight's lesson?

Dressage is hard, especially for me...