Consider upper respiratory tract infections, hyperthyroidism and inflammation among other causes for body heat while sleeping. 1. Upper respiratory tract infection: Cold, excessive fatigue and low immunity easily trigger upper respiratory tract infection, patients will feel cold, fatigue, and feel warm when sleeping. 2. Hyperthyroidism: Due to excessive production of thyroid hormones, the body’s metabolism is accelerated, and the body tends to be hot and sweaty when sleeping. 3. Inflammation: release of inflammatory mediators, stimulate the body reaction, raise the body temperature regulation point, resulting in increased body temperature, sleep body will have fever symptoms. If you can not determine the cause or fever symptoms are more serious, you should go to the hospital in time.