You’re sitting in a boring lecture, yawning and you accidentally fall asleep for a few minutes. You’re suddenly woken up by someone and now your sleepiness is completely gone. The following statements explain what happens here.
Adenosine is a neurotransmitter that your body naturally produces. It gets used in a lot of places, but one of those is in making you feel sleepy. Over time, it builds up and starts slowing down neurological processes, making you feel sluggish and sleepy.
When you sleep, the adenosine gets removed.
If you sleep for just a few minutes, you’re essentially taking the edge off without really solving the problem of too much adenosine. If you nap for 20 minutes, you take away a lot more adenosine. 30 minutes is pretty much the upper limit, because after that, your brain waves start slowing down a bit and you need some time to wake up afterwards (the groggy feeling). At that point, the next optimal nap length is 90 minutes because you complete one sleep cycle in that time.
Caffeine works primarily by blocking adenosine receptors, but once it fades away, you suddenly have all that adenosine that it had been holding back rush in to the receptors. This is a caffeine crash.
So, here’s how caffeine naps work:
You make a very strong cup of coffee (usually I go with two espresso shots) and drink it as fast as you can without burning yourself. 10 minutes is your target. Set your timer for 20 minutes (plus 5-10 minutes to fall asleep), and sleep in a dark room. When you wake up, you’ll feel great from the reduced adenosine levels. And since caffeine takes ~45 minutes to work, you’ll feel even more awake, since it’s blocking what adenosine is left.
If that isn’t an option for staying awake, one thing I’ve found that works is licking the roof of the mouth. It feels really weird, and will make you alert for a few more seconds with how unpleasant it feels. Not really suited to long lectures, but good for short (10-15 minute) meetings.
One thing is that it takes about 20-30 minutes before sleep inertia kicks in. That’s why you are told to take 20 minute power naps. Any longer can make you more sleepy.
Point is, those first 20 minutes are the most important for the actual feeling of being sleepy–at least, in the short term. You still need a full nights rest (even if you do get it in two chunks like in segmented sleeping).
Quick answer: google “coffee nap adenosine” or similar and read about how a caffeine nap works.
Depending on the duration of your nap, it could be adrenaline, or it could be your brain clearing out enough adenosine to make you feel more alert.
If it’s a “nod off for a few seconds and catch yourself before your head hits the desk” nap, then that’s almost certainly adrenaline.
If it’s between, say, 2-30 minutes, then your brain is clearing out some adenosine. Adenosine is a molecule that blocks nerves from transmitting signals, so as more and more of it is released in the brain, more of your brain is essentially being shut down, and you feel tired. When you sleep, adenosine gets removed and you feel more alert. Caffeine comes into play because it is a molecule similar to adenosine, and so caffeine molecules can sit on your nerve endings instead of adenosine, but caffeine molecules don’t stop the nerve from transmitting, so you remain alert. This is why a coffee nap is powerful. Caffeine blocks adenosine, you nap for 20 minutes to clear out some of the adenosine that’s already accumulated, and by not napping past 30 minutes you avoid deeper sleep that will make you groggy.
Disclaimer: Not an expert, may have butchered any science mentioned above, but that’s the general idea from what I have read.
It’s because of the jolt of adrenaline from being woken up. I was driving once well I was really sleepy (kids, don’t try this at home it is dangerous and stupid) and I started to nod off. Until I hit the rumble strip. I was awake alert and awake for a solid hour.
The same thing happens when you nod off in class, and your friend wakes you up.
It’s an evolutionary trait if something abrupt wakes you up. Say, a lion trying to eat you. It’s really important that you are awake and alert enough to escape the danger. Even though being eaten by a lion isn’t really a thing anymore it’s still very beneficial.