[dopylitty]

I have a theory that there are two variables that impact my subjective feeling of having a good night’s sleep.

The first is whether I wake up at the right part of the sleep cycle. For you that might mean 7.75 is when you’re deeply asleep while 7.5 or 8 might be a better time to wake up. Crucially for me it also means even if I get more than eight hours I still feel like garbage if I wake up and get out of bed at the wrong part of the cycle.

The second variable is how much sleep I get. I might wake up in the right part of the cycle but if I got 6.5 hours of sleep I start to drag, especially in the afternoon. That’s where avoiding activities like eating before bed or drinking alcohol helps. That’s also where doing a 4-5 mile run during the day (not too close to bedtime) helps because I’m more likely to maintain sleep for a full eight hours.

[robertlf]

That's interesting. I definitely think there's a cyclical aspect to it because my fatigue usually goes away in the evening around 6 p.m. or later.

[sizzle]

Second this, waking up in REM makes me groggy with brain fog all morning. I use a sleep cycle calculator every night.

[nradov]

Waking up in REM has zero effect on me. This might be an individual thing.