A hot flash is a sudden temptation of excessive heat that is not a result of something external. We do not exactly know why a hot flash occurs. It can be that variating estrogen levels disrupt your body’s temperature. As a result, the blood vessels close to your pores and skin open up, and your pores and skin temperature abruptly rises.
Source: https://vocal.media/psyche/anxiety-and-hot-flashes-what-s-the-relationship-between-them