When Jesse Jackson Jr.'s office described the missing congressman's medical condition Wednesday as "mood disorder," it attracted a little head scratching and at least some disbelief.
But a psychiatrist and mood disorder expert at Loyola University Medical Center says the ailment, medically speaking, is no joke.
"A mood disorder is not just being moody or moodiness," said Dr. Angelos Halaris. "Mood disorder is something more serious than just a temporary, short-lived fluctuation in one's mood. ... The person really becomes, to a greater or lesser degree, dysfunctional. "
About 15 percent of the population suffers from some type of mood disorder, including depression, dysthymic disorder or bi-polar disorder, Halaris said.
The worst-case symptoms if left untreated include memory trouble and even suicide, he said. Other severe symptoms are dysfunction to point of inability to go to work or do routine life chores.
Halaris said he knows of other congressmen and senators who are treated for mood disorders and suspects it might have affected a president or two as well.
"If stress, literally, piles up, and the person feels that there's no hope or no end in sight, they cannot see the light at the end of the tunnel," he said.
A statement released Wednesday noted the congressman is responding positively to "intensive medical treatment at a residential treatment facility."
The congressman’s office added that rumors about Jackson Jr. being treated for alcohol or substance abuse "are not true," but a family friend told NBC News that he has severe clinical depression, a drinking problem or a problem with alcohol.
The friend said he's being treated at a facility in Arizona, which Halaris said doesn't come as a surprise considering warmth and sunshine can play a role in recovery.
"Timing is critical," he said. "We could be looking at weeks to months, perhaps even many months, even a year, depending on the severity of the condition until the individual is able to return to a fully functional life again."
Jackson's family remains mum on the congressman's exact ailment. His father, Rev. Jesse Jackson, said Thursday he is "hopeful" for the recovery..
"As a father, I offer no medical diagnosis, only the unconditional love of his family," he said.