How Long To Nap

This is all well and good for people who can fall sleep right away, a 20 minute nap would mean an hour alarm since it would take 40 minutes before there is a possibility of napping.
Everyone is different though.
- I will eternally be jealous of people who can fall asleep immediately and/or nap. Just falling asleep is like a 30-40 minute endeavour on a good day :(
- True that everyone is different, but out of curiosity have you tried a 20 minute catnap before? What was it like?
  A lot of folks don't really get to sleep in a proper sense when taking this short of a nap, but even though they're still conscious they reap the energy benefits from the rest - more so than taking a more traditional break.
  
  Yes, and sometimes I can nap, other times I just “rest my eyes” for about an hour.
  I have ADHD, so for me my mind just wanders, even if I’m tired. If I can focus my mind and have it wander on a single thought it seems to be easier to doze off though.

This data is pretty dated. Your brain compensates. There's something called REM rebound to where if you don't get enough sleep, your brain will offload as much REM as possible to the end of your sleep, filling in the missing and crucial sleep cycle.
- How does your brain know when the end of your sleep is?
  
  Is your brain a separate entity? You literally decide when to wake to with alarm. Or if you don’t set a time, it wakes you after x hours, after it’s backloaded all the REM.
  If sleep deprivation gets too bad, it’ll completely knock you out to get as much REM in as it feels you need to function, alarm or no alarm.
  
  Weird polyphasic sleep schedules take weeks to start working, so probably from patterns. Although if what op comment is true something else is happening too
  
  Billions of years of evolution

Hmm I have my suspicions that this isn't accurate

For me its just groggy regardless of duration
- Have you been checked for sleep apnea?
  
  Well now I'm going to ask about it
  
  i plan on getting checked for it as soon as I have the money. It’s definitely possible
- Agree, any duration nap is a day ruiner

How about my 4 hour depression naps?
- See if you can do 6 a day
  
  You can't be depressed if you're unconscious!
  
  "Drink away the part of the day that I cannot sleep away"
  
  That will interfere with my 16 hour sleep.

I wish there was an alarm that could actually detect when I fall asleep and wake me up at the appropriate time afterwards, rather than just trying to guess how long it will take to get to sleep and setting the alarm that way
- Sleep as Android can do this

Naps are poison to me, even a short nap means I'm gonna be up far past my usual bed time and makes the next day absolutely miserable. I'm jealous of people that can get in a good nap and still keep their normal sleep schedule.
- That's our secret, we can't sleep a normal sleep.

For me the key to a refreshing nap is not breaking it with an alarm. I can sleep 30mins or over an hour at noon and if I wake up naturally I need 5mins to "get sober" and then I am super refreshed. If I Set an alarm that wakes me up at a certain time during my nap I need waaaay longer so feel awake.

My brain when I try to nap: "4 hours, take it or leave it."

Imagine being able to sleep for just a nap instead of sleep through every alarm for 6 hours
- i literally have 5 alarms on my phone and 2 on my smartwatch and IT DOES NOTHING

My grandmother used the keys-in-hand method. Sleeping on a couch with one arm with keys outwards. Once the hand let the keys fall she woke up. That was apparently perfect for her sleep cycle.
- Interesting. I suspect keys would not be enough to wake me up...maybe a bowling ball...
  
  I'd need the bowling ball to start a Rube Goldberg machine that flips me off the couch.
  
  Now try to see if you can hold a bowling ball for the duration of trying to fall asleep
  
  well, seems there's a market for a small hand-held thingy that sets off an alarm when it hits the ground!

Yes, so set that alarm just before you fall asleep!

I'm not very convinced at least about the grogginess. Usually for me is mostly random, and the reason that I don't risk any kind of nap unless I don't feel a bit obliged.

Narcoleptic here. Not bad, but I'd jus..... lik.....t ..ad......zZzZzZZZZZzzZZz..zZZZZz
- Yep, straight to REM before my eyes close. No nap length feels good either. Even those adrenaline inducing micro-naps while driving.
  Now with meds, naps aren't even an option.

Why not eternity?

This seems completely wrong.
Yes at 1:30 you are in deep sleep, as it is believed we sleep in roughly 3 hour cycles, where if undisturbed you'll go for another 3 hours.
But that also means if you wake up after 1.5 hours, or really too early into sleep beyond 20-30, you're going to wake up all groggy and hating yourself. Anecdotally I've always made sure to sleep at least 3 hours, even if I had 4 hour of time, I'd sleep 3 and it made it so much easier to wake up.
And for those who have trouble falling asleep, I suggest to stop using falling-asleep time to gather your thoughts and relax. If you need just close your eyes at another time and do it then to clear you mind (which is what meditation is), do that. Your body is a machine that needs to be turned off in steps, like a computer. You control all the knobs.
- Sleep cycles are 90-110 minutes, so your entire comment is pretty much invalid.
  
  lol that whole comment is confidentlyincorrect material.
  Somebody read the “about” page on their sleep tracking app and fancies themselves an expert now.
  
  I don't see how the part about how to better fall asleep is "invalid" because I got it wrong. I did say it seems, based on the fact I thought cycles were 3 hours. I looked it up and I'm thinking of polyphasic sleep.
  My anectode still works because I was sleeping 2 cycles. So at best, part of my comment is "wrong", and that's without taking into account I wasn't saying anything other this "seems wrong".
  This is what these discussions are for, if you don't like it go back [removed] on /r/science