Sleep terms you think you know but actually don’t

Both REM sleep and non-REM sleep are important


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  • The information provided in this article—and the sleep score registered through Pokémon Sleep—does not represent or substitute for a diagnosis from a physician or health care professional, and it cannot be used as a diagnostic or therapeutic treatment for a sleep disorder. Users should seek medical attention in case they present signs or symptoms that could be associated with sleep disorders.
  • Please note that the information in this article is intended for adults regarding sleep unless otherwise stated.

Sleep is divided into two different types: REM sleep and non-REM sleep.

REM stands for Rapid Eye Movement, and REM sleep refers to the times when someone’s eyes are moving actively around during sleep. Non-REM sleep is used to describe the times when such activity is not present.

During both REM sleep and non-REM sleep, our brains behave differently than when we are awake.

About REM sleep

Because we often dream during REM sleep people tend to think that sleep is shallow, but in fact it’s about as deep as stage two or three of non-REM sleep, as described below.

Also, it was recently discovered that our brains are more active during REM sleep than they are when we’re awake.

About non-REM sleep

Non-REM sleep is divided into three stages based on the depth of sleep.

Sleep Stages】​

  • Stage 1: Relatively shallow sleep. A dozing state.
  • Stage 2: Fully asleep. It accounts for much of the total sleep duration.
  • Stage 3: The deepest stage of sleep. We almost never dream while we’re in this state.

REM sleep and non-REM sleep are completely different types of sleep, so we can’t say that one is more important than the other. In order to refresh our brains and help keep our bodies healthy, it’s important to repeat plenty of sleep cycles to get both types of sleep.

About Dr. Yanagisawa

Masashi Yanagisawa

Born in Tokyo in 1960, Masashi Yanagisawa completed his medical doctorate at a graduate school in the University of Tsukuba and is a member of the National Academy of Sciences. In 1987, he discovered the vasoconstricting peptide endothelin while in graduate school, and in 1988 he discovered orexin, a neuropeptide that regulates sleep and wakefulness. At 31 years of age, Professor Yanagisawa came to the United States, where he presided over laboratories at the University of Texas and at the Howard Hughes Medical Institute over the span of 24 years. He founded the International Institute for Integrative Sleep Medicine (WPI-IIIS) in 2012, establishing it under the Japanese Ministry of Education, Culture, Sports, Science and Technology’s World Premier International Research Initiative. Professor Yanagisawa founded S’UIMIN Inc. in 2017 and currently acts as CEO.

He supervised the provision of sleep-related information during the development of Pokémon Sleep.

He was awarded a Japanese Medal with Purple Ribbon in 2016, received the Asahi Prize and the Keio Medical Science Prize in 2018, was named a Person of Cultural Merit in 2019, and received the Breakthrough Prize in 2023.