(Health.com) -- People who have trouble sleeping rarely see their problem as an illness that requires treatment, or as an acceptable reason to call in sick. That mind-set may be hurting employers and employees alike by compelling people with insomnia to drag themselves to work and sleepwalk through the day, a new study suggests.

Researchers surveyed 7,428 employed people across the U.S. and found that 23% experienced some form of insomnia -- such as difficulty falling asleep or nighttime waking -- at least three times a week during the previous month, for at least 30 minutes at a stretch.