Fluff up your pillows! Today (and tonight) is National Sleep Day.

There's not much history as to how this holiday came to be -- but, being the "sleep evangelists" we are, we'd never pass up the opportunity to celebrate the power of shuteye. Maybe that means taking a little afternoon nap today, setting up a more sleep-friendly environment or committing to a New Year's resolution for better sleep (there's still time!).

Even if you didn't have the luxury of sleeping in this morning, you can still "celebrate" by brushing up on the most recent research findings about sleep and your health. Here's what we've learned about sleep since last year's National Sleep Day.

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  • Not Enough Sleep Could Increase Stroke Risk

    Getting <a href="http://www.huffingtonpost.com/2012/06/11/sleep-stroke-risk_n_1586837.html">fewer than six hours of sleep a night was linked this year with an increased likelihood of stroke</a> -- even in people without the usual risk factors, like smoking, a lack of physical activity, or high blood pressure. This connection may be due to short sleep's impact on these other factors, like increasing blood pressure or altering hormones, Fortunately, sleep is what's called a "modifiable risk factor," meaning people can control how much they get, thereby (potentially) controlling the risk of serious health consequences.

  • Getting Too MUCH Sleep Can Also Hurt

    Most research focuses on the problems of getting too <em>little</em> sleep, but <a href="http://www.huffingtonpost.com/2012/03/27/sleep-heart-problems-too-much-too-little_n_1380730.html">overdoing it can also cause problems</a>, at least for the heart, according to a study published in March. Researchers found that people who slept eight or more hours a night had a higher risk for cardiovascular problems including stroke, congestive heart failure and heart attack.

  • Too Little Sleep Leads To Poorer Eating Choices

    Researchers have long known that too little sleep can lead to weight gain, but in the last 12 months, scientists have taken a step toward understanding <em>why</em>. In one study, researchers found that areas of the brain that help us weigh the factors in deciding to eat a certain food were affected by too little sleep, <a href="http://www.huffingtonpost.com/2012/06/12/sleep-and-diet_n_1581940.html">making it harder to come to the conclusion to reach for healthier fare</a>. Another study tracked responses to images of unhealthy and healthy foods and found that on the nights participants got just four hours of sleep, they experienced greater activity in the reward and motivation areas of their brains, suggesting increased vulnerability to the unhealthy picks and poor decision making. While future research is still needed, since both studies were small, the results build upon a body of earlier research linking little sleep to wider waists. Some even came from earlier in 2012, including one study that found that <a href="http://www.huffingtonpost.com/2012/03/14/sleeping-calories-eat-study_n_1345232.html">skimping on sleep leads to more calories consumed throughout the day</a>.

  • Sleep Deprivation Affects The Immune System Similarly To Stress

    Serious stress takes a physical toll on the body, and recent research suggested that a lack of sleep can produce the same effect. A July study found that <a href="http://www.huffingtonpost.com/2012/07/03/sleep-immune-system-stress-deprivation-white-blood-cells_n_1643641.html">white blood cell counts jumped</a> when participants were sleep-deprived in the same way they do in response to stress.

  • Sleep Can 'Turn Off' Obesity Genes

    If we could truly sleep ourselves thin, maybe we wouldn't all be so sleep-deprived. But one 2012 study did bring us a little bit closer to understanding how more sleep can keep us thin. "The longer you sleep, the less important genetics become in determining what you weigh," Dr. Nathaniel Watson, co-director of the University of Washington Sleep Disorders Center, told HuffPost in May. "Does this mean you can sleep yourself thin?" Watson asked. "Probably not. But you can <a href="http://www.huffingtonpost.com/2012/05/01/sleep-obesity-genes-fat_n_1465483.html">sleep yourself to a point where environmental factors, like diet and activity, are more important in determining your body weight than genetics</a>." Among more than 1,000 pairs of twins, the researchers found that short sleep "turned on" genes related to body mass index, while sleeping nine hours or more seemed to keep those genetic influences on weight at bay.

  • Skimping On Sleep To Study Could Mean Worse Grades

    Plenty of students have tried the all-night cram approach to acing a test, but research from this year suggests skipping sleep to study puts students on the fast-track to failure. Los Angeles-area high schoolers were asked to record how much time they spent sleeping and studying and then note when they had trouble in class or received a bad grade. The researchers found that <a href="http://www.huffingtonpost.com/2012/08/23/sleep-study-grades-deprivation-academics_n_1822229.html">the more a student passed up on sleep in order to study, the worse he or she did in school</a>. "Although these <a href="http://www.eurekalert.org/pub_releases/2012-08/sfri-sst081412.php">nights of extra studying</a> may seem necessary, they can come at a cost," study researcher Andrew J. Fuligni, a professor at UCLA and senior scientist at the university's Institute of Neuroscience and Human Behavior, said in a statement.

  • Sleepy Surgeons Mean Risky Procedures

    It's no surprise that the long hours medical residents work would leave them feeling fatigued. But for the first time, research this year attempted to measure <a href="http://www.huffingtonpost.com/2012/05/21/sleepy-surgeons-new-study_n_1534410.html">how that fatigue translates to risk for error</a> -- and the findings were bleak. "Fatigue levels were higher than anticipated, especially on the night float rotation," study co-author Dr. Frank McCormick, of Harvard Combined Orthopedic Residency Program and Massachusetts General Hospital, told HuffPost in May. On average, the surgical residents who participated in the study were functioning at 80 percent of their mental capacity nearly half the time they were awake, and at less than 70 percent nearly 30 percent of the time.

  • Sleep Deprivation Ups Anxiety

    We all feel a little anxious from time to time, but a study from June found that getting too few winks can raise anxiety levels, thanks to <a href="http://www.huffingtonpost.com/2012/06/11/sleep-deprivation-anxiety-uc-berkeley-study_n_1582321.html">magnified anticipatory reactions in the brain</a>. "What this study highlights is the importance of sleep for healthy emotional functioning," Andrea Goldstein, who did the research at the Sleep and Neuroimaging Laboratory at the University of California, Berkeley, told HuffPost in June. "And people who are highly anxious may actually be more vulnerable."