Idiot's guide to sleep: Chapter 2 - How we sleep

Read Chapter 1: Why we sleep

When you sleep, your body cycles between two types of sleep, REM (Rapid Eye Movement) or non-REM. We'll get more into REM during another chapter, but for now understand that the difference between REM and non-REM sleep is excruciatingly basic. Either your eyes are zippin' like a Vegas slot machine, or they're not. Not exactly rocket science.

When you're body is in a non-REM cycle, it is going to be in one of four stages. A whole non-REM cycle will last anywhere from 90-120 minutes.

Stage 1: It's that drowsy, I'm somewhere between being awake and being really deeply asleep. You're out of it, but not entirely.

Stage 2: A period of light sleep. Your muscles are contracting and relaxing intermittently, the heart rate is slowing and your body temp is dropping. It's at this stage that the body prepares to enter deep sleep (which I envision is sort of like NASA's central command when it prepares to launch a space shuttle).

Stages 3 & 4: Deep Sleep (but not dreaming sleep). During these deep sleep stages of non-REM sleep, the body is repairing and regenerating tissue, building bone and muscle mass, strengthening the immune system.

After non-REM sleep, you'll have a short burst of REM sleep, which as I said, we'll dive into more later.

One sleep cycle will then look like this.

1. Stage 1 (non-Rem)
   
2. Stage 2 (non-Rem)
3. Stage 3 (non-Rem)
4. Stage 4 (non-Rem)
5. Stage 2 (non-Rem)
6. Stage 1 (non-Rem)
7. REM SLEEP

Think of it like putting your clothes in washing machine. First they soak, then they spin, then they may soak and spin again, and the final two stages are the clothes getting rinsed of all the soap and then the basin drains all the water out. It's not like you just throw your clothes in, they sit for an hour and then are clean. The machine puts them through various stages to complete its wash sequence to get the clothes clean.

Your brain/body does the same thing during sleep. Each night your mind uses sleep as a way to sort of reboot. To do this, you go through a series of sleep stages, consisting of either REM sleep or non-REM sleep.

And just like you can't do all of your laundry in one load, your body can't complete all of its tasks in one cycle, so the cycle noted above will repeat in that order throughout the night.

Okay, there will be a 10 question true/false quiz over this material on Monday, any questions?