This homeostatic system functions like an hourglass that counts how long we’ve been awake, slowly building up pressure for us to sleep. The longer we stay awake, the more sleep pressure we accrue from the accumulation of molecules such as adenosine left behind when the brain expends energy. Then by sleeping, we reset the hourglass, primarily through NREM sleep. Overall, the homeostatic system helps balance the time we spend awake versus asleep, and if we are up too long, it will eventually override our circadian systems and help us recover lost sleeping time.
