Swelling of one eye after sleeping on one’s back is usually caused by the pressure on the eyelid of one eye when sleeping on one’s back, and the obstruction of venous blood and lymphatic fluid reflux, in addition to the allergy of the patient’s eyelid skin is also one of the common causes. When patients sleep on their stomachs, it usually leads to eyelid compression, which may cause the venous blood vessels and lymphatic vessels inside the eyelid to become narrowed due to pressure, causing venous blood and lymphatic fluid return obstruction, so that plasma or lymphatic fluid leakage to the eyelid subcutaneous tissue space, resulting in edema of the patient’s eyes. When sleeping on the stomach, if the patient’s eye skin comes into contact with bedding and other attached cotton wool, skin debris and other allergens, it may also trigger an allergic reaction, thus causing the patient’s eyelid swelling. It is recommended that patients with swollen eyelids seek prompt medical attention to assess their condition and follow the doctor’s instructions for treatment.