Your body fires an alertness signal right before bedtime
In the two to three hours before your usual bedtime, your internal clock pushes out a strong wake-up signal, sometimes called the wake maintenance zone. It's the hardest stretch of the whole day to fall asleep, which is why an early-evening nap so often fails. Counterintuitively, this last burst of alertness is the runway your body needs before the lights-out drop kicks in.
