But it's still hard because during sleep, we have much lower levelsof norepinephrine....

But it's still hard because during sleep, we have much lower levels
of norepinephrine. That's a chemical messenger
that causes us to feel awake and alert. And in the brain,
it helps us form memories. Our levels of another chemical,
serotonin, plummet too. And it looks like that when
serotonin release is shut off, it biases the brain to think
that whatever it's