Stage 3 in the sleep cycle is the deep sleep stage. This is the stage of sleep that puts your body in recovery mode, This is where your mind and body slow down, blood pressure is reduced, heart rate goes down, and you are completely calm and relaxed. Overall brain activity slows down in this stage.

When people are speed time in this stage of this, they wake up feeling refreshed. Other ways to describe deep sleep are below:
sleep like a log
slept like a baby

The opposite of deep sleep is light sleep. This is when you toss and turn all night and wake up tired even if you slept for over 7 hours.
My sleep tracker says I had over 2 hours of deep sleep last night. Amazing!

or

I need to read up on ways to get more rest vs sleep so that I can spend more time in deep sleep.
by Dilemmas.co February 8, 2021
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A sleep that will take a while to wake up from.
I was in a deep sleep, so I woke up and hour late.
by TheDerpo May 27, 2015
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Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning. It occurs in longer periods during the first half of the night. Your heartbeat and breathing slow to their lowest levels during sleep. Your muscles are relaxed and it may be difficult to awaken you. Brain waves become even slower.

REM sleep first occurs about 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids. Mixed frequency brain wave activity becomes closer to that seen in wakefulness. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels. Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams. As you age, you sleep less of your time in REM sleep. Memory consolidation most likely requires both non-REM and REM sleep.
The pineal gland, located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down. People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day. Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.
Deep sleep
by ... Zjdbckdnznsjd September 17, 2019
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