The fact that co-pilot Andreas Lubitz crashed Germanwings Flight 9525 into the French Alps, killing 149 people and himself, suggests that, were major depression to blame, it had spiraled down into the worst form: psychotic depression.  The official diagnostic name for this is “Major Depression, Severe, With Psychotic Features.”

Major depression itself, of course, can cause suicidal ideation.  Tragically, in 2013 alone, there were 41,149 reported suicides in the United States, making suicide the 10th  leading cause of death.  

But depression linked to taking the lives of others is far more rare.  We think of cases like that of Andrea Yates, who drowned her five children in a bathtub in 2001.

Even when people have reached the lowest levels of mood and energy and concentration and sleep and appetite and have lost their will to live, they almost always maintain their empathy for others and desire to safeguard them.  Indeed, it is not uncommon for depressed patients to bemoan the fact that they would like to end their lives, but cannot rationalize inflicting onto loved ones the suffering that would result from their suicides. Those who do take their lives often leave notes apologizing to those they leave behind, and speaking of their unbearable suffering.

When depression spirals even further downward, however, and sparks psychotic features in the people vulnerable to that class of symptoms, all that can change.  I have treated more than one person whose depression led to delusional beliefs that plots were unfolding that threatened not only that person, not only that person’s family, but all of humanity.

How could Major Depression, Severe, With Psychotic Features have figured into the crash of Flight 9525?

Depression with psychotic features can prompt someone to believe that crashing a jet is actually saving the passengers from a worse fate, when the world ends in an unspeakable calamity of suffering.

Depression with psychotic features can cause what are called “command auditory hallucinations,” in which those afflicted feel powerless not to obey the voices they hear.  And the voices can instruct them to commit unspeakable acts.

Depression with psychotic features can even cause a pilot to believe that the people flying with him aren’t people at all, but secret soldiers being flown to their destination to take over that country.

I am not asserting that any of these thoughts or experiences influenced the behavior of Mr. Lubitz.  I cannot know that.  But I know that human beings are vulnerable, when they are most severely depressed, to such thoughts and feelings.  And when they are, a seemingly innocuous phrase uttered by someone can seem steeped in dark meaning and fuel their psychosis even more. 

I have had a patient suffering with depression with psychotic features interrupt our discussion, and ask, “When you said I could take any chair I wanted in the office, were you saying you think I should go to the electric chair?  Why would you think that?”

I hospitalized him.

Again, I don’t know the inner workings of any depression that might have afflicted Mr. Lubitz.  But it is certainly possible that an errant turn of phrase uttered by his co-pilot before leaving the cockpit got twisted through the distorted lens of psychotic depression and made crashing into the French Alps seem like the only thing to do.

Dr. Keith Ablow is a psychiatrist and member of the Fox News Medical A-Team.