Why is it so much worse in cold weather.

I just went from a tropical country 30°c to like 10°c windy as hell.

The nerve pain is about x 2 of anything I've experienced. Researched online and its normal? My first winter with sciatica.

Beyond fatigued and nauseous too. Can barely work. How do people in cold countries manage this, I am so sorry. So miserable right now. Worried about the next ~ 2 months of this cold weather.