It can lead to depression and even suicide.

The so-called ‘psychotically depressed’ person who tries to kill herself doesn’t do so out of quote ‘hopelessness’ or any abstract conviction that life’s assets and debits do not square. And surely not because death seems suddenly appealing. The person in whom Its invisible agony reaches a certain unendurable level will kill herself the same way a trapped person will eventually jump from the window of a burning high-rise. Make no mistake about people who leap from burning windows. Their terror of falling from a great height is still just as great as it would be for you or me standing speculatively at the same window just checking out the view; i.e. the fear of falling remains a constant. The variable here is the other terror, the fire’s flames: when the flames get close enough, falling to death becomes the slightly less terrible of two terrors. It’s not desiring the fall; it’s terror of the flames. And yet nobody down on the sidewalk, looking up and yelling ‘Don’t!’ and ‘Hang on!’, can understand the jump. Not really. You’d have to have personally been trapped and felt flames to really understand a terror way beyond falling.

Killing oneself is, anyway, a misnomer. We don't kill ourselves. We are simply defeated by the long, hard struggle to stay alive. When somebody dies after a long illness, people are apt to say, with a note of approval, "He fought so hard." And they are inclined to think, about a suicide, that no fight was involved, that somebody simply gave up. This is quite wrong.

Depression is a painfully slow, crashing death. Mania is the other extreme, a wild roller coaster run off its tracks, an eight ball of coke cut with speed. It's fun and it's frightening as hell. Some patients - bipolar type I - experience both extremes; other - bipolar type II - suffer depression almost exclusively. But the "mixed state," the mercurial churning of both high and low, is the most dangerous, the most deadly. Suicide too often results from the impulsive nature and physical speed of psychotic mania coupled with depression's paranoid self-loathing.

(...) Since I was a kid."
"Which you refer to as 'back when you were happy.'"
"Right.

Its so hard to talk when you want to kill yourself. That's above and beyond everything else, and it's not a mental complaint-it's a physical thing, like it's physically hard to open your mouth and make the words come out. They don't come out smooth and in conjunction with your brain the way normal people's words do; they come out in chunks as if from a crushed-ice dispenser; you stumble on them as they gather behind your lower lip. So you just keep quiet.