4. Brain Uses More Energy
The majority of energy produced while awake (about 80 percent) is used by various physical activities such as movement, breathing, and speaking. While asleep, this energy is obviously not being used and the “energy surplus” is diverted to the brain.
This means that the brain’s energy consumption is actually higher in certain stages of sleep, such as REM, than it is while awake. This energy is put to good use, completing secretarial tasks that are backlogged while awake, such as creating and strengthening neural connections and removing waste products.
The brain is too busy during the day with more urgent and energy-hungry tasks like decision-making for these other activities to occur. During sleep, however, the brain has some “free time” to tidy up.
3. Lose Weight
Ever wake up to find you are suddenly very thirsty? This is because your body actually loses more than 0.5 kilograms (1 lb) of water to the surrounding air at night.
Think about it this way: The air inside your lungs is hot—about 36.7 degrees Celsius (98 °F). It is also filled with moisture. Since most people’s rooms are much cooler than 36.7 degrees Celsius (98 °F), the air you breathe out as you sleep contracts as it cools, drawing moisture out of the air and your body.
The weight of the lost water is minuscule, only about 0.02 grams per breath. But over the course of the night, this can add up to more than 0.5 kilograms (1 lb) of lost weight.
CO2 has a similar but lesser effect. Everyone knows that you breathe in oxygen (two atoms) and breathe out carbon dioxide (three atoms). As one more atom is coming out than going in, an infinitesimal amount of mass is lost each time you take a breath.
However, there are about a billion trillion carbon atoms in each breath you exhale, so this adds up to about 0.7 kilograms (1.5 lb) every night. This happens in the day, too, but you more than replace the water and carbon through food and drink.