Sometimes when I wake up from a nap, I don't even know whether I fell asleep in the first place. As a person who doesn't take naps as a habit, I need to take efficient naps when I'm tired and need rest.

How to know if (or when) I fall asleep, and not merely just lying there doing nothing?


3 Answers 3


"How to know if (or when) I fall asleep, and not merely just lying there doing nothing?"

Sleep Retrograde Amnesia:

Retrograde amnesia refers to the loss of memory for things preceding a certain event. When we talk about retrograde amnesia in the context of sleep, this event is sleep onset.

You not remembering has to do with your short term memory not working during sleep.

  • You could video tape yourself sleeping and this would show you when you appeared to drift off to sleep.

  • You could also monitor your pulse and Blood Pressure to see when you went to sleep. Blood pressure and pulse are generally lower when you sleep so if you monitor your pulse when you are asleep you can possibly approximate the time you fell asleep.

  • You could try having motion sensor lights and when you stop moving they shut off. Maybe you can remember them shutting off, maybe not.

If you think you have a sleeping disorder then you should consult your doctor, she/he may order a Sleep study.

Polysomnography (sleep study)

used to diagnose sleep disorders. Polysomnography records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study.......usually is done at a sleep disorders unit within a hospital or at a sleep center. You'll be asked to come to the sleep center in the evening for polysomnography so that the test can record your nighttime sleep patterns. Polysomnography is occasionally done during the day to accommodate shift workers who habitually sleep during the day.

  • 1
    How can blood pressure be measured during sleep without waking up the patient? Feb 15, 2016 at 4:42
  • 3
    @CountIblis I wore an ambulatory BP monitor for 24 hours recently. Although you're certainly aware when it takes a measurement because it inflates the cuff, it did not awaken me once.
    – Carey Gregory
    Feb 15, 2016 at 5:08

Modern smartphone apps offer this information. A smartphone has a gyroscope built in, and when you lay it on the mattress close to your body, it picks up tiny movements. As you fall asleep, your musculature relaxes, and the app knows how to distinguish the movements of a person in deep sleep, light sleep, and lying awake. It provides you with a record of your sleep cycles for the night.

It is probably not perfectly accurate, but I find it quite good from personal experience. It certainly can distinguish between times when I lay awake, trying to fall asleep (and not noticeably moving) and times when I am really asleep. I can't say how good it is for hypnogogic states, and it can be fooled somewhat if you are concentrating on not moving while awake (e.g. if you are doing a muscle relaxation exercise or meditating). But for normal sleep, it gives you a nice record.

I have no peer reviewed sources on this, so will have to give you a commercial link: Sleep as android is the app I use, but AFAIK there are several per platform. If you have a fitness tracker such as Fitbit, it might offer a similar functionality - there are headbands specifically for sleeping, probably more accurate than a smartphone (but also more intrusive).


If you want to know the exact moment you fell asleep do the following: Place a steel/metal plate on floor by the bed. Hold a spoon in your hand lay down to sleep keeping the hand in way your palm is exactly above the plate. When you fall asleep, the spoon will drop on plate and make a sound, waking you up.

You can check the timing before going on bed and after waking up to see how much time did you take to fall asleep. On average it takes 7 minute.

PS: Artist Bali used this spoon-plate method to take micro naps and wake up to paint his creativity.

  • 1
    Knowing how much time they need to fall asleep on average isn't really going to help with knowing if you slept at all and how much, though. There really are people who often fall asleep within minutes and then the next day they need an hour.
    – YviDe
    Feb 16, 2016 at 13:57
  • This is a fresh insight, that I had no idea of. Nice answer. @YviDe, has a very valid point, however. Hence, Bali's method won't be welcome in OP's particular case :-(
    – user19679
    Feb 18, 2016 at 2:46

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