Trying to sleep // Trying to sleep - © G.P. Kidd|Getty Images(© G.P. Kidd|Getty Images)

Do you have trouble getting a good night's sleep? Don't blame insomnia or stress. Instead, you may be afraid of the dark, finds new research presented today at SLEEP 2012, the 26th annual meeting of the Associated Professional Sleep Societies in Boston.

In the study, participants who reported being good sleepers or poor sleepers were placed in both well-lit rooms and dark rooms. When the lights were on, both the good sleepers and bad sleepers reacted similarly to sudden noises. But when the lights went off, the two groups behaved differently. The good sleepers became accustomed to the noise bursts. The bad sleepers, on the other hand, grew more anxious and easily startled. (Can't figure out what's keeping you up at night? Read 5 Sleep Mistakes You Don't Know You're Making.)

In the past, researchers assumed a poor sleeper is tense when the lights go down because he associates his bed with a night of tossing and turning. Now, researchers wonder if many poor sleepers might have an untreated phobia.

How do you know if you suffer from insomnia or a fear of the dark? Some tell-tale phobia signs include always keeping a light or the television on while you're in bed, tensing up when you enter a dark room, or thinking of awful things happening--like someone breaking into your house--when you're in darkness, says study author Colleen Carney, Ph.D., author of Quiet Your Mind and Get to Sleep: Solutions to Insomnia for Those with Depression, Anxiety or Chronic Pain.

While being afraid of the dark might conjure up memories of Dad searching for monsters under the bed when you were 5 years old, it can be a serious problem as an adult. Lack of sleep or poor-quality sleep depresses the immune system, causes mood swings, and spikes hunger hormones, says Carney. (Getting adequate sleep can also keep your waistline trim, past research has found. Want more great weight-loss tips? Pick up Dr. Travis Stork's The Lean Belly Prescription.)

Unfortunately, you can't treat this phobia like you would insomnia, she explains. If you do, it might actually make your fears--and subsequent sleep--worse. Conventional insomnia treatments usually require the patient to leave the room and come back to bed when he or she feels calmer. But avoiding the darkness will only increase your phobia. "You could inadvertently be training yourself to be afraid of the dark," says Carney. That's why a white noise machine to block out sudden sounds or a night light aren't good ideas either.

So what will help? Try entering dark rooms during the day or hit the sack with someone by your side, suggests Carney. Do this until you feel your anxiety decrease in those situations. Then, work your way up to being in a completely dark room alone for short periods of time. (Find the hidden causes of your body's other aches and pains. Here are The Real Reasons You're Hurting.)