It’s a rite of passage for incoming, doe-eyed college freshmen and a weekly occurrence by the time finals arrive in May. All-nighters mark the full surrender to academic demands — as if to look sleep square in its marshmallowy face and tell it, unafraid, “I’m too busy for you.”

But college students (and the rest of the sleep-deprived-on-purpose world) aren’t invincible, despite what truckloads of caffeine may suggest. Sleep is important. And getting none of it, let alone an hour too little, throws your body’s regular processes for a loop — jostling the delicate balance of hormones out of whack and signaling to your brain that something is definitely wrong. A number of things happen when you pull an all-nighter, and not one of them is good.

Your Memory Suffers

The latest theories proposed by sleep research implicate sleep as serving the critical function of flushing out waste that accumulates in your brain during the day. You’re bombarded with all sorts of sensory information, most of which you’ll never use. So like a garbage truck that disposes of the waste material during the night, your brain uses the resting state to export the unused cerebral spinal fluid from your brain, through your bloodstream, and to your liver, where it can be processed as waste.

Avoiding sleep stops this process from happening. Waste material builds up, your memories never have time to concretize (consolidate, to the folks in lab coats), and new information essentially goes in one ear and out the other. While many bleary-eyed students will attest to a heightened short-term memory the day of the big test, in the long run the results are the same: Information is digested only for as long as it’s needed; then it’s promptly regurgitated, never to be remembered again.

You Get Fat

Keeping your appetite in check are two key hormones: leptin and ghrelin. Leptin tells your brain you’re full. Ghrelin says you’re hungry. And a 2004 study suggests that all-nighters may stop leptin production in its tracks, elevating ghrelin levels, causing participants to eat more and gain weight.

Normally when you sleep, the metabolic processes responsible for digesting food and converting it into energy work in the background. But depriving your body of adequate rest also deprives it of the ability to regulate body weight. And to make matters worse, the foods you start craving aren’t kale chips and celery sticks.

“Food consumption remained normal in sleep-deprived rats fed protein-rich diets, but increased 250% in rats fed calorie-rich diets,” the researchers wrote. “Sleep deprivation may thus increase not only appetite but also preference for lipid-rich, high-calorie foods.”

Your Immune System Fails

Anyone’s who’s pulled an all-nighter knows that feeling groggy is often coupled with a sickly malaise. It’s hard to put your finger on, but it’s dangerously close to the start of a cold. Immediately sleeping to recharge often suppresses the budding illness, but sometimes it doesn’t. And that comes as no surprise to sleep researchers.

“A lot of studies show our T-cells go down if we are sleep deprived,” Dr. Diwakar Balachandran, director of the Sleep Center at the University of Texas M.D. Anderson Cancer Center in Houston, told WebMD. “And inflammatory cytokines go up,” which “could potentially lead to the greater risk of developing a cold or flu.”

This is the same principle behind resting when you’re already sick. The less work the body has to do to fight infections, on top of the laundry list of normal tasks it’s asked to complete, the better job it can do at eradicating illness.

You Elevate Disease Risk

In the same vein as upping your risk for illness, the chances of contracting major diseases also elevates after an all-nighter. Though the big names like cancer, high blood pressure, and diabetes normally result from prolonged sleep deprivation, the added stress on the body — in the form of poor diet and overtime demands — can effect short-term malfunctions in as little as one night.

A 2011 study found that obese participants faced a greater risk of high glucose levels (hyperglycemia) and low insulin levels when they were sleep deprived than when they achieved a health amount of sleep. The researchers speculated that their findings could apply to all adolescents, not just obese teens.

You Lose Sense Of Emotions

One of the stranger, yet equally problematic effects of pulling an all-nighter lies in your psychology. In addition to ghrelin and leptin spiking, your levels of cortisol (the stress hormone) rise, too. A study conducted by researchers at the University of California, Berkeley, found that sleep-deprived people lack “emotional rationality.” In real terms, this is the difference between learning the fridge is empty and feeling mild disappointment, and learning the fridge is empty and exploding with rage.

Researchers believe there is a natural brain circuitry that governs your emotional responses. When you don’t sleep, this circuitry has the tendency to short-circuit. Something misfires. “It therefore seems that a night of sleep may ‘reset’ the correct brain reactivity to next-day emotional challenges by maintaining functional integrity” of the correct neural pathways, the team points out.

In the end, a full night’s sleep may only leave you feeling well-rested, but that feeling is actually concealing multiple complex, highly-connected processes that need sleep to function. Still don’t think an all-nighter can hurt you in the long run? Sleep on it, and reconsider in the morning.