It depends on how much the conditions changed from what kind of riding you have been doing. But it's a lot more work to do the same speed or the same distance in the cold. Did it get a lot colder all of a sudden? Did you try to keep the same pace as if it was a lot warmer?

You may have to just take it easier than you thought until you get used to it. Go slower if you have to. This would have happened to me a few times but I already was very familar with pre bonk symptoms. I think you have it right.