system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does sleep deprivation cause extreme tiredness instead of burning more calories to support the energy usage throughout the day?
gpt
After being deprived of sleep for long enough the body will begin to "replace" sleep with calories. Your body still needs the sleep of course but it begins to do what it needs to do to continue working. If you ever want to see this in action, it is common among the crab fishing crews in the Bering Sea. I've seen it explained a couple few times on there by both the crew and on board medical staff. Those men consume ridiculous amounts of calories, both to stay mentally alert, with the lack of sleep, and because the insane amount of physical labor they perform.