Sudden drowsiness may be related to physiological factors such as long-term sleep deprivation, or it may be caused by brain lesions or heart diseases. 1. Physiological factors: if long-term sleep deprivation will lead to the brain can not get enough rest for a long time, over time there will be dysfunction and so on, which may show sudden drowsiness, and may be accompanied by always sleepy, body weakness and other symptoms. 2. Brain lesions: common in encephalitis, meningitis, acute cerebral infarction or cerebral hemorrhage and other diseases, may affect the patient’s wakefulness center, resulting in sudden drowsiness, may also be accompanied by dizziness, headache and other symptoms. 3. Heart disease: commonly seen in myocardial ischemia, arrhythmia, atrioventricular block, etc., may lead to insufficient blood supply to the heart, causing impairment of consciousness, thus causing sudden drowsiness, which may be accompanied by panic attacks, weakness and other manifestations. Sudden drowsiness may also be associated with other factors. If symptoms persist, seek medical attention as soon as possible for targeted treatment.