1. You're always hungry. Your brain gets energy from food and sleep. If it's lacking energy from sleep, it'll compensate by getting it from food. Your stomach will produce more ghrelin, the hunger hormone, so you'll feel hungry—so hungry all the time that you can't help but indulge.
2. You're gaining weight. Precisely because of #1. The ghrelin stimulates your appetite and makes you crave fatty or sugary food. Yikes.
3. Your skin is breaking out. Your cells, including your skin cells, need to repair themselves. They repair themselves when you're asleep. When you're not getting any of that, the entire process, along with your hormonal balance, is disrupted. You'll not only get acne but your skin will also age faster.
4. Your sex drive is at a standstill. Lack of sleep can lead to low energy, fatigue, and sleepiness. It can then affect your libido or decrease your interest in sex.
5. You're moody or emotional. If you're sleep-deprived, you become grumpy and cranky, which can affect your personal relationships and your social life. You're also overreactive so it's so easy for you to be sad, be angry, or to cry.
6. You're clumsy. Sleepiness slows down your reaction time and motor skills. When you're sleep-deprived, you can't really process things (including your movements and your surroundings) very well.
7. You're forgetful. Your brain has sharp wave ripples that consolidate memory and put them in the neocortex, the part of the brain where long-term memories are stored. The sharp wave ripples occur in deep sleep, and when you're sleep-deprived, your sleep doesn't get very deep.
Also, when you're tired from lacking some shut-eye, you're not really paying enough attention to your surroundings enough to make an impression or memory.
8. You easily get sick. You immune system suffers when you lack sleep. While you sleep, it's in charge of producing cytokines, proteins that help protect you from infections. If you're not sleeping enough, you're not as protected so you're more likely to catch a cold.
9. You're having trouble seeing. When you're sleepy and tired, you can't control your eye muscles very well. The ciliary muscle, which helps your eyes focus, is easily exhausted. And the extra ocular muscle, which moves the eyeball, doesn't track as well, resulting in muscle imbalance and double vision.
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