In the first of a four-part series "The Science of Sleep", NY1 Health & Fitness reporter Kafi Drexel explains why many city residents are tired.

Surveying almost anyone on the streets of New York, you'll quickly realize it really is the "City that Never Sleeps.”

“I take sleeping pills. I'm not even going to lie,” said one New Yorker. “I have so much on my mind that once it's bed time, I lay down and everything attacks me.”

“I hate it. You wake up at 5:30 in the morning and you don't have to be up at 5:30 in the morning, and you just sit there and utter multiple curse words and shake your head and toss and turn and you can't get back to sleep,” said another.

But it's not just the Big Apple. Some sleep experts liken us to a nation of "walking zombies" because of the amount of rest we're not getting.

According to the National Center on Sleep Disorders Research, between 30 and 40 percent of adults say they experience symptoms of insomnia at some point each year, and for many it's a chronic condition.

“Most people don't talk about it. They tend to ignore it,” says Dr. Carl Bazil, a neurologist at New York Presbyterian-Columbia Medical Center. “They figure, ‘Well, everyone's tired. Everybody has trouble sleeping.’ And doctors are the worst. Doctors won't ask about it. They'll ask about every other health problem. They won't ask about your sleep. And people don't bring it up, so sleep problems are the most under-diagnosed of any medical illness.”

Aside from it impacting your daily performance and making you super moody, lack of sleep can actually have a serious impact on your overall health.

“We have a sleep crisis in America. We treat sleep as a luxury, but it is a necessity,” says social psychologist Dr. James Maas of Cornell University. “Sleep plays a major role in risk for hypertension, heart attacks and strokes, obesity, type-2 diabetes and even cancer.”

According to the National Sleep Foundation, how much sleep you really need changes with age and the individual. School-aged children, five to 12 years old, need about 10 to 11 hours of sleep; teens, 11 to 17 years old, need about 8.5 to 9.25 hours of sleep; and most adults need between seven and nine hours of sleep.

Just like practicing good body hygiene, experts say you can spend less time counting sheep by practicing good sleep hygiene.

“The most important concept of good sleep hygiene is your bedroom environment. You can't just flick a switch and expect to go to bed,” Bazil says.

There are some simple things you can do to improve chances of a good night's sleep, including going to sleep and waking at the same time every day; using your bedroom only for sleep; cutting back on chocolate, caffeine, nicotine and alcohol, which can disturb sleep; and coming up with a relaxing bedtime routine – like substituting a warm bath for late-night television or web surfing. These activities can often set your clock back to day-time mode.

Still having trouble reeling the sand man in? Don't fret. We'll take you through the A, B, Zzzzs of it coming up in Part 2 of the series.