Why do we feel tired if we sleep excessively?

Question

When we eat, finally we feel full. I know which mechanism causes the sensation of being full. But when we sleep excessively we often still want more sleep. Why does this happen? Is there a mechanism underlying this?

Answer 1

The sensation of feeling full after eating and the desire for more sleep despite excessive sleep are both influenced by complex physiological processes and mechanisms involving hormones, neurotransmitters, and the regulation of bodily functions. Let's explore each situation:

1. Feeling Full After Eating: The sensation of feeling full after eating is regulated by several factors, including hormones released by the digestive system and the central nervous system. The stomach and intestines release hormones like cholecystokinin (CCK) and peptide YY (PYY) in response to food intake. These hormones signal to the brain that the stomach is full and promote satiety.

Additionally, the hormone leptin, produced by fat cells, plays a role in appetite regulation. As fat stores increase, leptin levels rise, sending signals to the brain that help regulate hunger and energy balance.

2. Desire for More Sleep Despite Excessive Sleep: The desire for more sleep despite excessive sleep (known as "sleep inertia" or "sleep drunkenness") can occur for several reasons:

1. Sleep Cycles: Sleep is organized into cycles, each containing multiple stages, including rapid eye movement (REM) and non-REM sleep. If you wake up from a deep sleep stage, you might experience sleep inertia. It takes time for your body to transition from the deeper stages of sleep to a fully alert state.
2. Circadian Rhythms: Circadian rhythms, which regulate our sleep-wake cycle, can influence our alertness and sleepiness at different times of the day. Oversleeping might disrupt these rhythms, leading to grogginess and the desire to continue sleeping.
3. Sleep Debt: If you have been consistently sleep-deprived, excessive sleep might reflect your body's attempt to compensate for the accumulated sleep debt.
4. Neurotransmitters: The balance of neurotransmitters like serotonin and dopamine plays a role in wakefulness and sleepiness. Oversleeping might disrupt this balance, affecting your overall sense of alertness.
5. Sleep Disorders: Conditions like sleep apnea, narcolepsy, and certain medical conditions can lead to excessive sleepiness even after prolonged sleep. These disorders can interfere with the quality of sleep, causing persistent drowsiness.

It's important to note that individual responses to sleep and wakefulness can vary widely due to genetic factors, lifestyle, and overall health. If you consistently find yourself excessively sleepy despite sufficient sleep, it's a good idea to consult a medical professional to rule out any underlying sleep disorders or health issues.

Answer 2

There's no one answer to this question (the brain is too complicated for there to be only one answer to many questions!). But here are three possibilities worth considering:

1) We cycle through various stages of sleep throughout the night. Each of these, in a sense, can be considered to have its own level of 'depth'. If you normally wake up out of stage 1 sleep, this is a light level of sleep and thus is easy to wake from. Sleeping longer than normal may lead you to awake directly from a deeper level of sleep, such as stage 4 or REM sleep, which would leave you feeling groggy.

2) Similar to above, your body has a circadian rhythm that dictates your energy and activity levels at various points in the day. This rhythm uses internal mechanisms of time-keeping, but also external such as sunlight in the morning. Disrupting this cycle by not experiencing sunlight at the time in the morning that your body expects it can have unexpected consequences on your energy level.

3) It is possible this is an example of a 'third variable problem'. In this case it would mean your sleepiness is not actually caused by your excessive sleep, but rather they are each the effect of some other cause that controls them both. Perhaps you slept excessively because you are sick, and that same sickness is causing your sleepiness the next day too.