Health experts say they are hardly astonished that the suspect in the worst mass murder ever at a U.S. military base is an Army psychiatrist — the very person who is supposed to be helping soldiers deal with the traumatic stress of war.

Maj. Nidal Malik Hasan, suspected of gunning down 13 and wounding 30 at the Fort Hood Army Post in Texas, treated soldiers at the Darnall Army Medical Center there after being transferred in July from the Walter Reed Army Medical Center, where he had worked for six years.

Dr. Robin Kerner, an attending psychologist who specializes in disaster anxiety at St. Luke’s-Roosevelt Hospital in New York City, said it’s not uncommon for individuals who work with traumatized patients to suffer the effects of "compassion fatigue."

"This guy was counseling people coming back from war and there is something called secondary traumatization, where the therapist gets traumatized from hearing all the terrible things that have happened to the people they counsel," Kerner told FoxNews.com.

The problem, she said, is that when this happens, many mental health professionals do not properly take care of themselves.

"There are a lot of things professionals who are working with trauma patients need to do in terms of self-care so as not to get traumatized themselves," she said. "Oftentimes, workers are so focused on helping others that they neglect to take care of themselves. The bottom line — we don’t take our own advice."

WARNING SIGNS

Hasan raised many red flags in the days and weeks before the shooting that indicated he was beginning to unravel, said Dr. Keith Ablow, a psychiatrist and Fox News contributor.

"I’m sure as the investigation proceeds that what will emerge is a portrait of someone showing multiple signs of growing psychological problems and was using a variety of techniques to deal with them, some of which may have backfired," Ablow said. "This is why obtaining any information on prescriptions he may have prescribed himself is important."

"Many times," he said, those prescriptions "can have the opposite effect on individuals and even trigger feelings of violence."

Ablow said some of Hasan’s red flags included the extent to which he expressed his desperation not to be deployed overseas; his feelings about his military career and how it conflicted with his Muslim religion; and his actions in the days leading up to the massacre, which included giving away his possessions and giving out copies of the Koran to neighbors.

"The fact that he had been giving away his possessions is something psychiatrists are always attuned to, because it does make you legitimately wonder whether this is someone who sees their existence coming to an end," he said.

Hasan had also turned against the wars in Iraq and Afghanistan, his cousin told Fox News. The 39-year-old wanted to be released from the military, and he had even hired a military lawyer to assist his efforts, Nader Hasan said.

A 2008 report by the American Psychiatric Association found that the wars in Iraq have caused heightened stress, depression and sleeplessness among military personnel and their families.

As a result, Kerner said, mental health professionals are seeing extremely high levels of post traumatic stress disorder (PTSD) and substance abuse among soldiers who return to the U.S. — a level that may have affected Hasan.

"I don’t think we understand as professionals and as a society the toll that listening to traumatic stories takes on the listener," Ablow said.

Retired Col. Terry Lee, who worked with Hasan at Fort Hood, said he frequently made "outlandish" comments.

"He said maybe Muslims should stand up and fight against the aggressor," Lee told Fox News. "At first we thought he meant help the armed forces, but apparently that wasn't the case. Other times he would make comments we shouldn't be in the war in the first place."

Lee said Hasan was a loner who kept to himself and didn’t socialize a lot with officers off duty or on duty.

"Again, we don’t know why he turned," Kerner said. "But if we’re going with the theory that he was suffering from secondary traumatization — what happens is that he might not have even been aware of the trauma he was suffering from."

Kerner said what often happens is that we ourselves don’t realize that we are impacted by our trauma work, but people around us start noticing behavior changes such as anger, isolation and disconnection.

"In a lot of these cases, rather than respecting someone’s boundaries, it’s more important to try to get this person to think in a way that’s more rational and to get them help right away," Ablow said.

FoxNews.com's Marrecca Fiore and The Associated Press contributed to this report.