system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our energy levels go down when we're depressed?

Depressed people I've seen generally feel more tired and fatigued than usual and end up sleeping more than usual. Why is this?
gpt
Depression in many ways puts your body through the same processes that a lot of physical illnesses do. One part of that is that both are associated with the release of what are called pro-inflammatory cytokines in your body. Like the name implies, these are chemicals that cause inflammation in your body. Evolutionarily speaking, what humans and other animals do when they are sick is retreat and rest. They retreat because they are weak and wouldn’t be able to defend themselves against enemies. They are fatigued because their body is fighting off whatever is making them ill, and sleep more to reserve their energy. A lot of other stuff can happen here as well, but essentially your body shuts down everything that is not necessary for your immediate survival (sex drive? being able to solve super difficult sudokus? you don’t need that right now!) Collectively these are called sickness behaviors, and they developed because they are adaptive for your survival. Only with depression things get a little trickier because there is no obvious virus or bacteria to fight off. But essentially you’re body is confused but trying to help the best it can: it can hear the alarm bells ringing, and the alarm signal sounds a lot like being physically injured.