We've all been there: you're sitting in your afternoon lecture, trying desperately to concentrate on your professor, when suddenly a wave of fatigue knocks you right out. You may be angry about missing out on that class when you wake up, but don't get down on yourself: this midday drowsiness can easily be avoided with a life-saving tool known as the 26-minute nap.

If you know me at all, you know how passionate I am about the 26-minute nap. Using this napping method has saved my life in college -- and it can save yours too.

Here's why this is the ideal nap length, according to a 1995 study from NASA: 26 minutes allows you just enough time to doze off before you fall into a deeper sleep, so you won't wake up feeling groggy and disoriented -- a concept called "sleep inertia." On the contrary, NASA says that sleeping for 26 minutes can improve performance by 34% and alertness by 54%, which can make all the difference during a long day of studying.

Let's break it down even further. It takes, on average, 10 to 20 minutes to fall asleep. This is why I recommend only taking a nap when you're tired -- doing so allows you to make the most of your 26 minutes. After about ten minutes, your body leaves stage one of non-REM sleep and enters stage two of non-REM sleep, characterized by a slowed heartbeat, relaxed muscles, and slowed brain activity. Stage two is considered the last stage of sleep before you enter a deep sleep, and it usually lasts about 15 minutes. So, the ten minutes that it should take you to fall asleep, combined with the 15 minutes of stage 2 sleep, brings us to about 26 minutes in total -- a nap that lets you maximize light sleep while ensuring you don't fall completely into the abyss.

As I mentioned earlier, the best time to take this nap is in the early afternoon, between 1 and 3 o'clock, right when that post-lunch fatigue kicks in. Or if you're like me, and one nap just doesn't cut it for the entire day, try taking two: one in the morning and one in the late afternoon. But remember -- only nap when you're tired.

Though it is easy to fall back on a nap (or two) every day, it's worth mentioning that nothing is more effective for feeling refreshed and combating stress than a good night's sleep; about seven hours is best.

In the meantime, take a 26-minute nap, and listen to that lecture for once.