Take a 10‑minute nap in the afternoon — don’t sleep half an hour

Cost: It costs nothing. Just set aside 10 minutes and find a place where you can lie down or recline.
In plain terms: A 10‑minute nap gives an immediate boost of alertness that lasts about two and a half hours. A 5‑minute nap provides almost no benefit, while a 20‑minute nap only starts to help after roughly half an hour. Sleeping 30 minutes brings on sleep inertia — you’ll feel groggy right after waking, making performance worse than if you hadn’t napped at all.
Benefit: After a night of insufficient sleep, a 10‑minute nap quickly reduces drowsiness, fatigue, and improves energy and mental performance; some of these effects persist for up to 155 minutes. A 5‑minute nap yields virtually no benefit, and the advantages of a 20‑minute nap appear only after 35 minutes. A 30‑minute nap first causes sleep inertia, so performance is actually poorer right after waking, before any improvement occurs.
Evidence grade: B
Sources:Brooks & Lack (2006). A brief afternoon nap following nocturnal sleep restriction: Which nap duration is most recuperative? Sleep. https://doi.org/10.1093/sleep/29.6.831
Notes: Only one laboratory study exists, and its participants were healthy young adults. If you can’t fall asleep, there’s no need to force it; there’s no research showing any benefit from simply lying down with eyes closed for 10 minutes. Naps longer than an hour have been linked to higher mortality and increased risk of coronary heart disease — see Section 2, Item 38 (keep naps under 30 minutes). 〔37〕