You’re beginning to reach a state of total relaxation, in preparation for the deeper sleep to come.” Stage 3 and Stage 4: ...

A board-certified sleep medicine specialist reviews the history of wearable sleep trackers and explains how clinicians ...

If you're dealing with sleep deprivation or are already feeling the side effects, it's helpful to know the stages first. Below are the warning signs of sleep deprivation and what to do about it.