Random bad legs/fitness?

[Kevin3182]

Hey everyone!
today i was cross country skiing which i do when the roads are too gnarly to ride and i just felt horrible. I ski/ride at least a few times a week if not more and generally feel fine and can do hard efforts, However... Today there was nothing there, i had the bonked feeling right out of the gate. Ive had this happen a few times throughout my time riding and im just curious as to what causes it and how to avoid it?
Thanks!

[Tapeworm]

Potential causes are legion. Diet, training prior, rest, hormone imbalance (vit D, especially those in winter atm.) Simply not enough info to really say. Maybe ask on a skiing forum?

[metal]

Low blood sugar combined with dehydration can easily do what is described.