Geriatrician, Hospitalist, Patient Advocate, Healthcare Educator

Sleep Explained

Photo by Gregory Pappas

With those of us that are wearing smart watches and tracking our sleep at night, it can get confusing with the sleep scores and breakdown provided. What we do know is that sleep is vital. Sleep is one of the most essential things to function and it is important to understand what sleep does for the body. After all, we do spend about a third of our lives sleeping. Sleep allows our bodies and minds to recharge to get us prepared for the new day and all that gets thrown at us in everyday life.

It is recommended that adults get about 7 to 9 hours of sleep a night. During this period, we go through different stages of sleep consisting of a sleep cycle. Each sleep cycle lasts 90 to 110 minutes long, giving us about 4 to 5 sleep cycles a night.

Sleep is divided into non-rapid eye movement(NREM) sleep ranging from stages 1 to 3 which accounts for 75% of total sleep and rapid eye movement(REM) sleep which is stage 4 of sleep and accounts for 25% of total sleep. Furthermore, stages 1 and 2 consist of light sleep and stages 3 and 4 of deep sleep.

Here is the breakdown:

Light sleep

Stage 1(NREM)

  • dozing off stage, we transition from wakefulness to sleep
  • lasts 2 to 10 minutes

Stage 2(NREM)

  • we spend about 50% of total sleep in this stage
  • lasts about 10 to 60 minutes
  • the start of muscle relaxation, slowed breathing, and heart rate

Sometimes, you may feel like you’re starting to fall asleep and then experience a sudden muscle jerk or contraction. This is called hypnic jerk or hypnagoic jerk or “sleep start”. This occurs in stage 1 or 2 of sleep. Hypnic jerks are a type of sleep myoclonus, are common and random.

Deep sleep

Stage 3(NREM)

  • lasts 20 to 40 minutes
  • brain wave activity slows down, delta waves begin to emerge so also known as delta sleep
  • respiration and heart rate slow down as muscles relax further
  • body temperature goes down, blood pressure drops

Stage 4(REM)

  • comprises about 20-25% of sleep
  • lasts 10 to 60 minutes
  • arrives about an hour to hour and a half after you go to sleep
  • first REM period lasts about 10 minutes.
  • each REM stage that follows gets longer and longer
  • eyes move rapidly
  • body becomes relaxed and voluntary muscles become immobilized
  • brain activity increases again, sleep spindles are seen
  • dreams occur

Deep sleep:

  • Is felt to be help consolidate and solidify the information you have learned in the daytime
  • Helps with creativity and insightful thinking
  • Sleep spindles and powerful brain activity help to transition short term memory to long term storage(helps capture memories)
  • Improves immune system, increases amount of immune factors and also sensitivity to those immune factors
  • Cells repair and rebuild to promote bone and muscle growth