Sleep terms you think you know but actually don’t

Sleep cycles are not necessarily 90 minutes


  • Pokémon Sleep is intended for entertainment purposes only and is not intended for use in detection, diagnosis, or treatment of any medical condition or disease.
  • 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.

When we fall asleep, we enter non-REM sleep first.

Non-REM sleep is made up of three stages of differing depths. When we progress from the shallowest (stage one) to the deepest (stage three), then return back to stage one, this completes a single period of non-REM sleep, after which we enter REM sleep.

​​Each of these recurring sets of non-REM and REM sleep is referred to as a sleep cycle.

The length and number of sleep cycles experienced varies from person to person. They can also vary widely depending on the day, or even within a single night. We often hear that a single sleep cycle lasts for 90 minutes, but this is merely an average.

​​You may have heard advice along the lines of “you should get up after sleeping for an amount of time divisible by 90 minutes,” or “you’ll find it easier to wake up when a sleep cycle has just finished”—but that is not necessarily correct.

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.