Your mood, thinking, and reaction time all suffer when you get sick
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A sick brain is a dumb brain. Well, a dumb-er brain anyway. Just as your body feels drowsy, achy, and drained of energy when you're under the weather, your ill noodle suffers a Lloyd Christmas-esque drop-off in its ability to think, feel, learn, and react.

Here, researchers explain exactly how the common cold screws with your head:

The Moment You Become Sick

As soon as your body detects an invading bug, your immune system kicks into action and triggers the release of several specific types of cytokines, shows research from Concordia College in Minnesota. These small proteins perform a lot of different functions, but they're basically your immune system's messengers, alerting your central nervous system that you're sick and need to mount a counter-attack.

Unfortunately, while they're triggering your immune system's defenses, cytokines also mess with your brain chemistry, explains Andrew Smith, Ph.D., a health researcher and psychologist at Cardiff University in the U.K. Research from the University of Illinois, Urbana-Champaign shows your mood is one of the first things to change when you catch a cold. Both men and women tend to get pissy and quick-tempered and experience something psychologists refer to as "negative affect," which is a fancy term for feeling crummy about yourself and life in general. (Related: 5 Easy Ways to Stay Cold- and Flu-Free.)

While You're Fighting Off Your Cold

Smith's experiments have found that the flood of illness-related chemicals in your head also screws with your mental performance, specifically alertness and reaction time. This may explain why people who are sick have problems behind the wheel. Compared to healthy drivers, sickies bump into more curbs and tailgate other vehicles while failing to detect collisions, according to another of Smith's studies. (Help your body out with this guide to getting over a cold fast.)

Your ability to synthesize verbal information also falters, research suggest, while changes to the activity in your brain's frontal lobes may lead to problems with your psychomotor functions, which includes coordination, strength, speed, and balance. There's also evidence from a University of Southampton (U.K.) experiment that being sick jumbles your brain's ability to store new information and memories. While people did fine on most memory tests, their performance suffered when it came to repeating tasks they'd learned while ill. (That means studying or learning a new job skill isn't going to go well if you're sick, the research hints.)

When You Feel Better

Thankfully, research shows most of your mental and psychological fogginess lifts along with your other cold symptoms. But, for reasons that science hasn't figured out, your reaction time is still slower a week after your illness passes, Smith's experiments have found.

Apart from killing your cold with lots of rest and plenty of fluids (and maybe trying these cold and flu home remedies), studies indicate there's not much you can do to offset the unfortunate brain drain associated with your illness. But at least when it comes to your alertness, Smith offers one simple solution: caffeine. His research shows a little coffee or other caffeinated drink can help sharpen your brain even when you're unwell.