“Sleep affects everything,” says Diedra L. Clay, PsyD, chair and associate professor of the counseling and health psychology department at Bastyr University, “emotional and mental capabilities, as well as our bodies’ functioning. Sleep is our body's way of regenerating, and without it, the system malfunctions.”

Those 40 winks – more or less – function like a "reset" button for the brain. During certain sleep cycles, the brain classifies and "files" what was learned during waking hours and enables the brain to retain the information after waking. That explains the feeling of being unable to concentrate and the "fog" that descends on the mind the day after a sleep-deprived night.

Those who suffer from depression may find it difficult to sleep; conversely, those who suffer from sleeplessness are more prone to depression. A 2005 Sleep in America poll found that those who were diagnosed with depression and anxiety were more likely to get less than six hours of sleep per night.

Being Sedentary

Working up a sweat regularly can do more than help you fit into those skinny jeans. The endorphin rush people talk about after working out is real. Endorphins are neurotransmitters that interact with pain receptors in the brain, suppressing them and creating that great feeling, much like opiods, which function the same way. That's a natural high you can enjoy risk-free.

Hitting the gym or simply a regular brisk walk a few times a week staves off depression as well. It doesn't have to be anything too strenuous – simply getting your body moving will do the trick.