Based on the body's biological rhythm (circadian rhythm), the most ideal time for a nap is between 1 PM and 3 PM when drowsiness sets in after lunch.

During this time, the body's temperature slightly drops, naturally leading to drowsiness. If you feel tired enough to take a nap, it's best to sleep for a short 20 to 30 minutes.

When we fall asleep, we go through cycles of deep and light sleep, with a typical sleep cycle lasting about 90 minutes. Therefore, if you take a 90-minute nap, you can complete one full cycle, which can help you feel less groggy when you wake up.

However, if you sleep for this 90-minute cycle after 4 PM, it can make it difficult to fall asleep at night and decrease the quality of your sleep. This is especially impactful for those trying to sleep around 11 PM to midnight.

Sleeping for 90 minutes definitely clears your head and is effective for recovering concentration and memory. Especially if you didn't sleep well the night before or are mentally fatigued, it can have a "reset" effect. However, there are also side effects like the following.

Delaying nighttime sleep: The pressure to sleep decreases, increasing the likelihood of tossing and turning at night.

Sleep cycle confusion: If you get into the habit of sleeping late in the afternoon, your biological rhythm can change, solidifying into a nocturnal pattern.

Connection to depression: If you sleep and wake up around sunset, the sun has set, your body feels sluggish, and a strange emptiness or depression can wash over you. This is quite a common phenomenon.

So, if you're tired, a 20 to 30-minute power nap is best. This allows you to wake up before entering deep sleep, keeping your mind clear and having less impact on nighttime sleep. If you absolutely must sleep for 90 minutes, it's recommended to do so before 2 PM.

If the pattern of sleeping at 4 PM keeps repeating, it may be necessary to check your daytime routine or sleep hygiene.

Consider whether you're going to bed too late at night or drinking caffeinated beverages too late, etc.

Usually, when the seasons change, nighttime sleep becomes irregular, and that fatigue can feel deeper.

So, even if you're tired, thinking "Ah, I'm so sleepy... should I lie down for just 20 minutes?" can be a wise choice.