There's a bit of medical jargon to describe this, but it's pretty antiquated: 'psychomotor retardation'. Definition from Wikipedia: 'Psychomotor retardation (a

There's a bit of medical jargon to describe this, but it's pretty antiquated: 'psychomotor retardation'. Definition from Wikipedia: 'Psychomotor retardation (also known as "psychomotor impairment" or "motormental retardation") involves a slowing-down of thought and a reduction of physical movements in an individual. Psychomotor retardation can cause a visible slowing of physical and emotional reactions, including speech and affect. This is most-commonly seen in people with major depression and in the depressed phase of bipolar disorder...' This was/is my most prominent symptom. I once sat in a chair for three days straight (fortunately I had a glass of water within arm's reach), during a two-ish week period where I couldn't summon the motivation to leave my house. It was godawful. I wonder if it's a vestigial evolutionary trait, particularly in the case of seasonal depression. It would make sense in some contexts: if you're a hunter-gather, resources are scarce during winter. Your chance of survival might therefore be higher if you expended as little energy as possible while waiting out the winter...