Ask anyone who has spent any significant amount of time with a toddler and they'll tell you that exhaustion doesn't always look how you'd expect. Sure, sleepy little ones yawn and get cranky when they're tired like the rest of us, but let them get even a little more sleep deprived and they enter a state much feared by parents--overtiredness.

Rather than act sluggish and sleepy, when overtired, little kids will run around with manic energy, bouncing off the walls and denying vehemently that they're tired. (Usually, until a massive tantrum makes it apparent they're actually exhausted to the point of near psychosis.) Kids even sometimes struggle to fall asleep when you finally wrestle them into bed, because they're so amped up at that stage.

It turns out, according to sleep science, adults are actually similar. Sure, if you're up too late the night before, you'll feel all the classic signs of being underrested (heavy eyes, yawning, etc.), but if sleep deprivation is cumulative, resulting from weeks or months of too short nights, your body will try to compensate and you might not necessarily feel classically sleepy.

Instead, you'll show these signs that your sleep deprivation has entered a more critical phase. If you see them, it's time to seriously consider revamping your sleep schedule.

1. You have a perpetual case of the munchies (and your waistline is starting to show it)

If you can't keep your hands off the carbs and candy, it's time to have a long think about whether you're really getting adequate shuteye. Health magazine spoke to Chris Winter, MD, owner of Charlottesville Neurology and Sleep Medicine, who explained the biology of sleep deprivation-related munchies.

Apparently, being inadequately rested can cause your body to produce more ghrelin, a hormone that makes you feel hungry and crave fatty and sugary foods in particular, and less leptin, the chemical that signals when you're full. "If the brain is not getting the energy it needs from sleep, it will often try to get it from food," he summarizes.

Needless to say, Winter adds, these changes--along with the slowing of the metabolism that also often accompanies inadequate sleep--can quickly lead to noticeable weight gain.

2. You get a jolt of energy around 9:30 p.m.

If it's approaching bedtime and you feel like you're flying, it's reasonable to think that your sleep deficit can't be that bad. But according to Rafael Pelayo, MD, a sleep specialist at the Stanford University Sleep Medicine Center, that's exactly the wrong conclusion to draw from your nighttime second wind.

"Your body is keeping you up for that last stretch of the evening so it can get you back into a rhythm," he explained to "What often happens is the patient who's been running on empty will promise herself she'll go to bed early. 'Early' rolls around and she feels fine, so she keeps getting things done ... but then ends up with only 6 hours of sleep (again)."

3. You're ecstatic (or weepy) at the drop of a hat

The same article asks readers to imagine this scenario: "The sun seems so bright and cheerful, the coffee tastes soooooo good, and that cat going nuts with the empty cereal box is just hilarious." Is this a sign you're wildly happy with your life? Perhaps, but it could also be a signal that you've become too tired to control your emotions.

The same could be said of feeling particularly dejected for no apparent reason. "Ever find yourself tearing up over an embarrassing TV commercial?" asks the Huffington Post. "A 2007 study found that sleep-deprived brains were 60 percent more reactive to negative and disturbing images."

4. You've suddenly become a klutz

It's not just your emotions that are harder to control when you're sleep deprived. It's your body, too. "Researchers don't know exactly why, but sleepy people seem to 'have slower and less precise motor skills,'" the HuffPo reports.

In fact, miss enough sleep and you could end up effectively as uncoordinated as a drunk person. "In one 1997 study, researchers found that a person who has gone for even one night without sleep is about as impaired on early morning hand-eye coordination as someone who has a blood alcohol level of 0.10 percent, also known as legally drunk," notes

5. Your skin definitely isn't looking its best

If you haven't had a breakout this bad since you were a teenager, it's time to seriously consider whether your sleep schedule might be to blame. Your skin can also register your exhaustion simply by looking older.

Board certified dermatologist Jennifer Reichel told Greatist that "poor sleep habits can start to make skin less firm and hydrated--in a word: older. We have cortisol to thank for that. The hormone spikes in people who are stressed and sleep deprived, and it can break down skin collagen, which stops it from being its usual smooth self."

6. Libido? What libido?

Sleep deprivation can take a severe toll on your sex drive, and not just because, at some point, the only thing you want to do in your bed is sleep. "For men, studies have found that sleep deprivation can lower levels of testosterone, which also lowers their interest in being intimate with their partner," Greatist reports.

7. You're less creative than usual

Creativity demands a lot of cognitive resources, and when you're sleep deprived you simply don't have that much mental horsepower to spare. You might start resorting to tired clichés to keep up your end of conversations, Greatist warns.

8. You can't shake that cold

"If you keep coming down with the sniffles--or can't seem to kick that never-ending case--you might want to assess your sleep schedule. A 2009 study found that people who sleep fewer than seven hours each night have almost three times the risk of catching a cold than people who slept for at least eight," HuffPo points out.

Why? The Health article offers some more details: "Your immune system produces cytokines while you sleep, which are proteins that help protect against infections and inflammation, meaning a few nights of poor sleep could lower your body's defenses against pesky viruses."

How many of these worrying signs apply to you?