My mom was hospitalized for gastric bleeding and almost cured. but gradually she becomes very negative and depressed and physically very weak, and falls asleep instantly and cannot be woken up by anyone. when she wakes up by herself 3-4 hours later, she says she does not sleep and can hear people calling her, but she cannot react. This happens nearly everyday. She had brain MRI and which is ok. My question is if serious depression can cause this kind of frequent deep sleep ?