Given the importance of hydration, and you are sure you were well hydrated, then you may be right that you were simply exhausted.  Sometimes we just underestimate the importance of SLEEP.  We think we can keep going and keep going and never give our bodies the chance to rejuvenate.  And we get up to the canoe country expecting it to do that for us, but we are already running on empty.  

OR. . . you may actually have had a "bug" of some kind and have been ill.  

Either way, it sounds like you made the correct decision, albeit it a very disappointing one.

There is always another year.  Stay well and try again.

Sorry to hear about your experience, though.  That's a bummer.