And if all that wasn't enough to keep you up at night, research shows that people who don't sleep well tend to snack more during the day, which causes them to gain weight, which interferes with their sleep, which causes them to eat more empty calories. It's a vicious, bleary-eyed cycle.

About the only ones who benefit from all this are the sleeping-pill makers, who earn billions off all our tossing and turning. Last year, U.S. sales of sleeping pills hit just over $2 billion for a record 59.5 million prescriptions dispensed for sleep aids, according to the latest figures from health care information company IMS.

Granted, all the recent economic upheaval is enough to give us nightmares, but still — this is depressing news. Not sleeping well can have serious consequences for both our mental and physical health.

So how about some good news?

There is a simple way to greatly improve your sleep without resorting to sleeping pills, which can have serious side effects and interact with other medications. A small but significant new study from Northwestern University School of Medicine found that a group of 17 sedentary adults, 16 of them women age 55 and older, reported a dramatic improvement in their sleep quality just by engaging in regular aerobic exercise several times a week.

The study, which will be published in the October issue of Sleep Medicine, focused on older Americans in contrast with most sleep-and-exercise studies, which involve younger, good sleepers, the authors noted.

The participants in the 16-week study all said that for at least three months, they had been having difficulty falling asleep and/or staying asleep. They also said they were often groggy or tired during the day, making it hard for them to function. They ranked their quality of sleep as "poor," giving it about a 10 on a 14-point sleep-quality scale, where anything above 5 indicates increasing sleep problems.

Next: 4 tips to beat insomnia. >>