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New research may leave you in the dark about whether you and your fellow Americans are getting the sleep you need. However, one thing is certain: If you’re cranky and dragging yourself through the day, you’re clearly not getting enough.

In one survey of nearly 20,000 adults in four states, one in 10 of the participants said he or she didn’t get enough rest or sleep on any day of the preceding month. Released on Feb. 28 by the U.S. Centers for Disease Control and Prevention, the study also found that people age 55 and older reported significantly fewer days of insufficient sleep than those 18 to 34 years old.

But researchers didn’t ask the participants how many hours of sleep they got each night, so “we don’t know how long these older people slept,” says Vahid Mohsenin, M.D., director of Yale University’s Center for Sleep Medicine in New Haven, Conn. “Nor do we know if they woke refreshed and if they functioned well during the day, which are hallmarks of a good night’s sleep.”

Meanwhile, the National Sleep Foundation polled nearly 1,000 people who work at least 30 hours a week for pay—44 percent of them were over age 50. The 2008 Sleep in America survey released on March 3 found that nearly two out of three reported a sleep problem such as trouble falling asleep, waking during the night or feeling tired in the morning at least a few times a week. Nearly half of those bleary-eyed respondents said they had problems every night, and alarmingly, more than 35 percent reported nodding off or falling asleep while driving.

In contrast to this picture of a sleep-deprived nation trying to stay alert, a University of Maryland study released March 12 reported that Americans ages 18 to 64 actually get as much shuteye today as they did 40 years ago—and possibly more.

The study, “Not So Deprived: Sleep in America, 1965-2005,” analyzed the “time diaries”—hour-by-hour accounts of the previous day’s activities—of 37,000 Americans from 2003 to 2005. They compared these findings with time diary research from 1965 to 2001.

The disparities in the studies are likely to stem from differences in how they were conducted and the questions asked. But whatever the surveys say, if you don’t wake up refreshed and ready to go, something’s amiss with your sleep.

“Waking up feeling tired is the same as leaving a restaurant feeling hungry,” says Rafael Pelayo, M.D., of the Sleep Disorders Clinic at Stanford University in Palo Alto, Calif. “It doesn’t make any sense.”

Without enough sleep, you can be grouchy, less clear in your thinking and clumsier in your motor skills. Over time, sleeplessness can lead to health problems such as obesity and heart disease. “Although we generally recommend between seven and nine hours of sleep each night, don’t think of sleep in terms of hours,” he says. “It’s the quality that counts.”

Poor sleep isn’t a normal part of growing older. If you feel you have a problem, tell your doctor.