The test for narcolepsy I took consists for lying in bed the morning-after of the overnight part of the sleep test, and falling asleep 4 times. If you can fall asleep 4 times, and if you go too quickly into REM sleep every single time, then you are a narcoleptic. Narcoleptics can fall asleep very easily and tend to go very quickly into REM, but they do not go very easily into the deepest stage of sleep, which is the stage the brain uses to rid itself of certain materials. So narcoleptics have a bit of a problem. Often, we can get what many would call a "decent" span of sleep. However, we may only spend a couple of minutes in the deepest stage of sleep, where we might really want more.
I own a Zeo sleep monitor, and the data that I got out of it corroborated what the sleep studies indicated: I get only a fraction as much of the deepest stage of sleep, compared to the average for my age.
So here's the problem: These "sleep hacks" that allow you to enter into REM sleep very quickly for "power naps" may be harmful to you in the long term. You may well never enter the deepest levels of sleep that serves important physiological functions for your brain.
She says Edison did the same thing too, but had a handful of ball bearings instead of a key.
Now if you were falling asleep while trying to meditate then you might not be sleeping enough in general.
If you're tired in the afternoon, you only need a literal moment of sleep to feel revived. You can do this by sitting in a chair, holding something in your hand (a key, in this book), palm down, with something beneath it on the floor (a plate, in this book) that will create some sound when hit. The instant you fall asleep, you drop the item onto the the thing on the floor, it wakes you up, you feel energized.