A short mid-day nap, which is called Qailulah, this is a Sunnah of Nabi (S.A.W). It is not necessary to sleep, but rather to lie down during the daytime for some time to relax.
Another Hadith mentions that Nabi (S.A.W) said, "Sleeping early in the day betrays ignorance, in the middle of the day is right, and at the end of the day is foolish."(Fath Al-Bari, p.73).
Another Narration mentions, "We used to offer the Jumua Salah with Nabi (S.A.W) and then take the afternoon nap. (Al-Bukhari)
"Relaxing once during the day is very conducive to total relaxation and sleep - once you crawl into bed for the night." [Kerner]
Previous research has shown that short daytime naps improve vigilance and cognitive functions, and are beneficial for memory consolidation. In particular, a nap as short as 10 min can improve alertness and performance for 2.5-4 hours. A recent study assessed the health effects of napping in 23,681 healthy Greek adults for an average of about six years. After controlling for potential confounders, the researchers concluded that those who napped at least three times weekly for about half an hour had 37% lower coronary mortality than those who did not nap
Insomnia is a medical problem affecting an increasing number of people nowadays, and is adding stress upon their stress. Practicing this Sunnah is a beneficial remedy to assist a person battling with insomnia. Resting for Qailulah is also helpful for staying up for Qiyam al-Layl (prayer in the night) Insha’Allah.
Doctor Geolick Oston, who has written many books writes, "If it was in my control I would close schools, factories etc and make everyone rest at this time as if this is observed then we would have less ill patients and people would be saved from many illnesses." The psychologist suggests that sleeping at this time refreshes the body, strengthening it and it is saved from many physical and mental illnesses.