Expert says these 2 factors wake you up at 3 a.m. — but this $0 hack is helping me sleep through the night

On the left, a woman lies in bed asleep in the dark. On the right, a close up of a reMarkable Paper Pure tablet covered in notes, lying on a mattress.

The brain doesn't come with an off switch, although I could use one at bedtime. My laptop is asleep, my phone is on do not disturb, but my mind is still buzzing away. These racing thoughts lead to bad sleep and 3 a.m. wake ups.

As Dr. Shelby Harris, psychologist with BetterSleep, explains, there are two big factors behind nighttime stress. And they're things none of us can avoid: the past and the future.