“If you take it longer than 30 minutes, you end up in deep sleep. Have you ever taken a nap and felt worse when you woke up? That’s what’s happening — you’re sleeping too long and you’re going into a stage of sleep that’s very difficult to get out of.” [x]
Sleep inertia is a physiological state characterized by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. The impaired alertness may interfere with the ability to perform mental or physical tasks. Sleep inertia can also refer to the tendency of a person wanting to return to sleep.
Studies by the Human Factors Division at NASA Ames Research Center have shown that a variety of factors influence the severity and duration of sleep inertia. One includes:
- Depth of sleep when awakened. After roughly 30 minutes, the brain enters into slow-wave sleep (deep sleep). Being awakened during this stage yields more sleep inertia than awakening from other stages of sleep. However, since one cannot predict accurately the stages of sleep that will occur within a nap, there is no physiological reason to try to limit the length of a nap. When one is sleep deprived, any sleep is good.
Source: Ultra Facts