Sleep is crucial to sanity.

Sleep disturbances can contribute to, aggravate, and even cause mood disorders and a host of other illnesses. Yep. The link between sleep deprivation and psychosis was documented in a 2007 study at Harvard Medical School and the University of California at Berkeley.

Using MRI scans, they found that sleep deprivation causes a person to become irrational because the brain can’t put an emotional event in proper prospective and is incapable of making an appropriate response.

If you’re not sleeping, your brain doesn’t have an opportunity to do all the stuff it needs to do without the constant interruption of tangential thoughts. The brain works night shifts. And when it doesn’t get all the work it needs to do done, well, it gets a tad irritable, like you do when you can’t get your work done. And it takes it out on you.

Moreover, your circadian rhythm—the internal biological clock which governs fluctuation in body temperature and the secretion of several hormones, including the evil one, cortisol—is like a high maintenance house guest: if you don’t give it what it wants, you will suffer the price.

Chronic sleep deprivation, especially, is therefore bad news.

It makes your spouse miserable, because tired folks tend to snap more easily and bite off innocent heads. It can affect your memory (“I’m sorry, dear cousin, what was your name?”) and your concentration (“I forget what I was just saying…. Oh yes, my concentration … It’s bad.”)

According to one recent study, sleep deprivation can cause a decline in cognitive performance similar to the intoxicated brain. That’s right! Drunks can reason and judge better than you if you’ve gone too long without getting some zzzzs.

And finally, sleep disturbances can make you gain weight. You eat more when you’re tired and stressed.