Sleep is a state of body and mind for rest. It is essential natural part of individual’s life for normal physical, mental and cognitive health. A good number of researches have been conducted on latency and exact time of sleep. Cultural associations at minor level are also noted. Apart from the cases of occupational compulsion, all suggestions lie with nocturnal sleep as it is also related to circadian rhythms, and light at wrong time may disrupt sleep.
Charak Sutrasthana 21/44 commands against the day-time sleep for normal physiological bodies in between 18 to 65 years, however, it is allowed during summer season. The reason is obviously evident that a greater variation is observed for sunrise and sunset time according to season in India, and the period of night is 4-5 hours shorter in summer compared to winter. Such duration variation results in less available optimum sleeping time in night and sleep loss is common. Medical observations also confirm that the common causes of daytime sleepiness are due to sleep deprivation, sleep apnea and sedating medications.
Increased hot climate may also disrupt the sleep during summer season. Researches reveal that the earlier onset and late wake-up time of sleep in winter is due to cool conditions. An observational study based on sleep duration, quality and location shows more nocturnal sleep in winter and autumn (Robbins et al., 2020).
Srimadbhagwadgeeta 6/16 (Geeta Press) specifies that optimum sleep is needed for perfect Yoga, it should not be more or less. An article published on 3rd March 2022 in Communications Biology supports this with T1 volumetric MRI data of 37,552 individuals. The volume of 46 brain regions was observed larger in individuals sleeping 6-8 hours daily. Investigations by distinguished researchers have proven the association of hypersomnia or lack of sleep with psychiatric and neurological disorders leading to alteration in pulmonary and cardiac conditions.
Still, scopes of researches remain to explore about the physiological changes based on seasonal variation, specifically related to neurological impacts as activation of specific neural circuit is triggering sleep and wakefulness.