Thanks everyone. In the cold it is my legs, hips, ankles that lock on me and make it near impossible to walk, my right worse than my left. I sort of slide my left foot because I can't lift it.
Sitting in the sun for too long on a hot day does make me more tired but my body moves better.

I'm lucky to live in a very temperate place the summers rarely get above 75 F but there are 2 months in winter that can get down in to the 30's.
We have had an very unusually cold winter so far. I makes walking my son to class each morning a real chore. It's an open hallway then add the fact that it's a slope and I almost fall everyday during the winter.