[natdempk]

I never knew this. How can someone determine how long their sleep cycle is? I’d love to figure out how long mine is.

[crooked-v]

A good sleep tracking device with an accelerometer can generally record light sleep vs heavy sleep periods. See worn devices like Fitbit Versa 2 or (with the new watchOS 7) Apple Watch 3 and later, or devices that sit on the mattress itself like Withings Sleep.