A new study finds high rates of disturbed sleep among current and former military personnel who served in Afghanistan during Operation Enduring Freedom or Iraq during Operation Iraqi Freedom.

Sleep problems were considerably more common and severe among those with post-traumatic stress disorder (PTSD), reports Military.com. PTSD is an anxiety syndrome that occurs after a traumatic event, such as combat or military exposure. Symptoms typically improve after three months of treatment, but for some people the problem continues for the rest of their lives.

Data from the Pentagon suggests that up to 20 percent of returning Iraq war veterans suffer from PTSD. Records from the Department of Veterans Affairs show that nearly 76,000 veterans of the current wars were diagnosed with PTSD between 2002 and mid-2008.

According to the AASM, most people with PTSD report having disturbed sleep, and suffer from severe nightmares in which they relive the traumatic event. Severe cases of PTSD may be treated with cognitive behavioral therapy and medications to improve sleep.