Here’s why humans feel more tired after a sleep
Have you ever experienced that groggy feeling after waking up? When humans feel tired, they often consider taking a short nap to boost their energy and maximize working efficiency. While taking a nap may give a good rest, people often realize they feel more tired after a nap.
This situation is called “sleep inertia” – a physiological state of incomplete cognitive or physical performance that occurs immediately after waking up. Typically lasting from 30 to 60 minutes, sleep inertia can last up to two hours, depending on how much a person is sleep deprived. The exact cause of sleep inertia is unknown, but there are several theories addressing this condition.
Adenosine is a neurotransmitter that elevates sleep drive released from the basal forebrain as energy is consumed by the body. According to the Sleep Foundation, the molecule gets removed from the brain during sleep and therefore typically exists at low levels upon awakening. Therefore, one of the theories states that sleep inertia can be attributed to high levels of adenosine upon awakening.
A more generally accepted theory pertains to the sleep cycle. During sleep, humans go through a repeated 90-minute sleep cycle consisting of four stages: NREM stage 1, NREM stage 2, NREM stage 3 and REM sleep. Delta waves, also known as small waves, are associated with deep sleep and most commonly observed in the NREM stages. Therefore, if an individual wakes up before a complete sleep cycle, or the end of REM sleep, they are more likely to have more delta waves, thus feeling tired.
Even though one could minimize the effects of sleep inertia by waking up after a complete 90-minute cycle, keeping track of time can be burdensome especially if the person wakes up at random intervals. To counter the effects after an incomplete sleep cycle, individuals could incorporate various solutions, such as intaking caffeine, using bright light, washing their face with cold water, or doing a quick exercise. However, these methods only have temporary benefits. Therefore, for a long-term improvement, people should consider implementing a healthy sleep schedule, one that happens regularly, properly, and sufficiently at night.
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