There are many conditions that can cause this to happen when you have obviously slept for a long time and are still very sleepy. The first thing to look at is that although you have slept for a long time, the quality of sleep is not good. Sleeping for such a long time may have been in a kind of light sleep period, that is, the more sleep the more tired, the more sleepy feeling. The second is that there may be a disease, such as idiopathic hypersomnia, this disease will sleep for a long time, not easy to wake up, and people will feel very sleepy, always want to sleep, and even if you let him sleep, he can still sleep again. It is generally difficult to wake up such patients, and even after waking them up, they do not feel refreshed and still feel very sleepy. There are other systemic diseases that can cause this kind of sleepiness even after a long sleep, such as problems in the brain, especially in the hypothalamus, tumors or other lesions. There are also diseases like hepatic encephalopathy, chronic renal failure, hypothyroidism can also cause sleepiness. There is also the use of drugs, such as alcohol, sedative-hypnotics, anticholinergics, antihistamines or antidepressants, which can cause a long sleep time and still feel sleepy and feel that they have not slept well.