What happens during sleep - good health with ResMed

What happens during sleep


Wondering what happens during sleep? Think of your body like a factory. As you drift off to sleep, your body begins its night-shift work:

  • Healing damaged cells
  • Boosting your immune system
  • Recovering from the day’s activities
  • Recharging your heart and cardiovascular system for the next day

We all know the value of sleeping well, and we’ve all experienced the feeling of being refreshed after a good night’s sleep (and the feeling of fatigue after a poor night’s sleep). But even though we know this, in our busy society, many of us are not getting the quality seven to nine hours of sleep our bodies need to perform these functions.

Understanding the sleep cycle

Understanding what happens during sleep also means understanding the sleep cycle. During the night, our bodies cycle through two recurring phases of sleep: REM (rapid eye movement) and NREM (non-REM or non-rapid eye movement). Both phases are important for different functions in our bodies. For example, a hormone that is essential for growth and development is only released in the last stage of NREM sleep.

If the REM and NREM cycles are interrupted multiple times throughout the night — either due to snoring, difficulties breathing or waking up frequently throughout the night — then we miss out on vital body processes, which can affect our health and well-being not only the next day, but on a long-term basis as well.

What happens if you don’t get enough sleep?

If your body doesn’t get a chance to properly recharge (by cycling through the two phases of sleep, REM and non-REM), you’re already starting the next day at a disadvantage. You might find yourself:

  • Feeling drowsy, moody or sometimes depressed
  • Struggling to take in new information at work, remembering things or making decisions
  • Craving more unhealthy foods, which could cause weight gain1

If this happens day after day, night after night, you can imagine the strain it would place on your, nervous system, body and overall health. So if you’re not sleeping well or not feeling your best, it’s important to consult your doctor.


  1. Studies show that sleepy people also tend to prefer high-carbohydrate, fatty foods. Morselli L, Leproult R, Balbo M, Spiegel K. Role of sleep duration in the regulation of glucose metabolism and appetite. Best Pract Res Clin Endocrinol Metab. 2010 Oct. Some of this research was supported by US National Institute of Health grants. 24(5):687-702