system
Given the following post, respond as if you're commenting on Reddit:
human
I hear people say they're "too tired to sleep" all the time. Is there any grain of truth in this phenomena?

Can you ever really be *too tired to sleep*?
gpt
It is not the actual tiredness that makes it hard to sleep, but rather that with sleep deprivation there is an increase in adrenaline and cortisol release, which disrupts sleep onset.  Furthermore, this phenomena may also have some explanation from the fact that a person who stays awake all night (studying for example) and then tries to sleep during the day, may have trouble with sleep onset due to their circadian rhythm.