Dr. Dale Needham, a critical care specialist at the Johns Hopkins University School of Medicine in Baltimore, said the PTSD symptoms lasted for up to two years.
"We usually think of PTSD as something you develop if you go to war, are sexually assaulted or suffer a similar emotional trauma," Needham said in a statement. "Instead, it may be as common, or more common, in ICU patients as in soldiers, but it's something many doctors -- including psychiatrists -- don't fully appreciate."
Dr. O. Joseph Bienvenu, an associate professor of psychiatry and behavioral sciences at Johns Hopkins who was the study leader, said physical weakness usually gets better, but these mental symptoms often just linger.
"We need to pay more attention to preventing and treating PTSD in these patients," Bienvenu said.
Bienvenu said the unusual thing about PTSD in ICU survivors is that they often experience flashbacks about delusions or hallucinations they had in the hospital, rather than events that actually occurred.
Having a life-threatening illness is itself frightening, but delirium in these patients -- who are attached to breathing machines and being given sedatives and narcotics -- may lead to "memories" of horrible things that didn't happen, Bienvenu said.
"One woman thought her husband and the nurse were plotting to kill her," Bienvenu recalled.
The findings were published online in Psychological Medicine.