You Sleep in Stages
When you first fall asleep, you typically have a sleep cycle that starts with the NREM (non-rapid eye movement) stage, before you progress into a deeper NREM 2 and then NREM 3 (also called slow wave sleep). You finally land in the rapid eye movement (REM) stage of sleep, which is the stage most of your dreams occur. All these stages happen between 90 to 120 minutes, after which you wake up for like a second (most times without even realizing it) and then begin stage 1 again.
Your Body Temperature Drops
This is why it’s so easy to fall asleep when in a cool room or after a cool shower. This coolness actually mimics what your body is doing naturally, making it easier for you to immediately sleep off, because while you sleep your core temperature drops. In addition, during the REM stage of your sleep, your body is unable to thermoregulate, so if you get cold, your body won’t shiver to build up inner warmth, until you’re awake.
You’re Temporarily Paralyzed
But only for a few minutes – like 20 minutes. This paralysis usually happens during the REM stage (where most of your dreams occur). It’s what sometimes prevents you from acting out your dreams. So you might be an action hero in the dream world, jumping up and down, fighting here and there, but in the real world you’re curled up on your side, sleeping like a baby. However, the paralysis doesn’t last for very long.
Your Body Regulates Hunger Hormones When You Sleep
This is why you feel hungry when you wake up after having poor quality sleep. Unfortunately, you tend to eat higher- calorie foods when you feel this hunger, leading to weight gain. Hunger-regulating hormones are unable to work as they should when you don’t sleep well, this is why sleeping well is recommended for those who either want to keep fit or lose some weight.
This is the feeling of falling you get as you’re falling asleep or sometimes when you’re even asleep. Sometimes you can start dreaming before your body has reached the REM stage, and these jerks might occur then, in response to you acting out a dream of falling on or tripping over something. Hypnagogic jerks are more likely to happen when you’re overtired, sleep-deprived or stressed, when your brain can aggressively enter into sleep cycles before your body has had a chance to catch up.