Robin Williams reportedly suffered from severe depression, addiction, and alcoholism before he killed himself at his California home Monday.

We may never know exactly when and how Williams arrived at the decision to commit suicide, but one of the saddest realities about suicide is that it often results from impulsive decisions that might have never occurred again if the person had survived or backed out.

Anywhere from one-third to 80% of all suicide attempts are impulsive acts, according to The New England Journal of Medicine. 24% of those who made near-lethal suicide attempts decided to kill themselves less than five minutes before the attempt, and 70% made the decision within an hour of the attempt.

Suicidal urges are sometimes caused by immediate stressors, such as a break-up or job loss, that go away with the passage of time. 90% of people who survive suicide attempts, including the most lethal types like shooting one's self in the head, don't end up killing themselves later. That statistic reflects the "temporary nature and fleeting sway of many suicidal crises," reports The New England Journal of Medicine.

A 1978 study of 515 people who were prevented from attempting suicide on the Golden Gate Bridge between 1937 and 1971 found after more than 26 years 94% were still alive or had died of natural causes.

Many rare survivors of Golden Gate Bridge suicide attempts recall regretting their impulsive decisions instantly — even as they were falling. A couple survivors who jumped from the Golden Gate Bridge told their stories to The New Yorker back in 2003, like then-18-year-old Kevin Hines who jumped in 2000 after pacing on the bridge for a half hour while passersby ignored him.

He finally jumped based on the thought that "nobody cares."

"My first thought was, 'What the hell did I just do? I don't want to die,'" Hines told The New Yorker.

Then-28-year-old Ken Baldwin, like Hines, chose to hurdle over the bridge's railing rather than stand on it first because he didn't want to lose his courage to jump. Although he was severely depressed on that day in 1985, he changed his mind the moment after his leap. "I instantly realized that everything in my life that I'd thought was unfixable was totally fixable — except for having just jumped," he said.

That indecisiveness is explained by suicidologist Edwin S. Shneidman, according to a review of his works by Antoon Leenaars:

The prototypical psychological picture of a person on the brink of suicide is one who wants to and does not want to. He makes plans for self-destruction and at the same time entertains fantasies of rescue and intervention. It is possible — indeed probably prototypical — for a suicidal individual to cut his throat and to cry for help at the same time.

The period where the chance of lethal suicide is at its highest and most dangerous is relatively short, typically just hours or days rather than months, according to Shneidman.

Of course, not all suicides are impulsive, as some are the result of extensive planning and conviction. Impulsive suicide involving decisions made in as little as five minutes is one of two types generally seen among patients suffering from depression, according to Dr. Charles Nemeroff.

The other type involves "the sort of classic notion that, I've been hopeless and helpless for so long. I'm hopeless that I'll ever be better, and I'm helpless to do anything about it," Nemeroff said. That type often includes planning, notes, and goodbyes.