How do we know when we need sleep?

How do we know when we need sleep?

What drives sleep is how long one has been awake. We suspect that various compunds in the brain accumulate to the point where they're trying to drive the brain along and get it into a state of sleep. But you have to be in a situation where sleep is appropriate and also the biological clock has to agree that it's the right time, so you get this mixture of things going on. But the thing to always keep in mind is the pressure for wakefulness which drives the pressure for sleep and what the biological clock is saying which will enable sleep to happen.