sleep stage

{
  "id": "MLC-T-ONC-007814",
  "term": "sleep stage",
  "field": "Oncology and biomedicine",
  "definition": "One of four stages of the sleep cycle based on the type of brain activity that occurs during the stage. Stages one, two, and three occur during non-rapid eye movement (non-REM) sleep, which is when a person first falls asleep and then moves from a light sleep into a deep sleep. Stage four occurs during REM sleep, which is when the eyes move rapidly while closed and when most dreams occur. During normal sleep, a person goes through four to five sleep cycles that last about 90 minutes each and include both non-REM sleep and REM sleep.",
  "references": [
    "NCI Dictionary of Cancer Terms"
  ],
  "url": "https://mlchart.com/terminology/oncology/sleep-stage/"
}