It's hot, and I feel dizzy and nauseous when I sleep at night. Why? Heatstroke or something?

Slight heatstroke. You had heatstroke before you turned on the air conditioner, but it took you some time to react. Sweating is your body's self-regulating function. As long as you don't have a high fever, there won't be any big problems. If the appetite is normal, it will get better soon. If you have no appetite, take some heatstroke prevention treasure, and you will want to eat it after 2 hours. Taobao sells them.