@Fredex, I do this exactly: My brother said he could kill a cold in one day. He said to put on some socks, sweatpants and a shirt, crawl into bed and lay there for 24 hours

Except I don't get a shiver, during sleep I usually will feel my body temp ascend several degrees, stay high for an hour or so, and come back down. I will wake up feeling cooled and well-rested. Next day whatever it is/was is gone.

Regarding wearing a mask in China, I was there for two weeks in 2019. Dirtiest shithole I have ever been to. After 3 days, my throat burned constantly from the smoke and pollution. Just awful.