system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why does it sometimes get harder to fall asleep the longer you stay awake?
gpt
Tiredness and wakefulness are two independent states influenced by your circadian rhythm.

Your body produces melatonin to help induce sleep, as controlled by the circadian rhythm. This peaks around 3am for a normal adult lifestyle. Past this peak, melatonin production ceases and your liver breaks down what was produced. Your body becomes more alert, though is still fatigued.