Why did Meriwether Lewis try to kill himself?

Answer 1

Meriwether Lewis was a troubled individual, and not suited for the bureaucratic life after the expedition. He found himself deep amongst petty and jealous administrators. On the way to Washington to clear his name, he stopped at Fort Pickering at the Chickasaw Bluffs. Those there described him as mentally distressed.

Three weeks later, he was found in his rooms with two gunshot wounds at a roadside inn at Grinder's Stand, Hohenwald, Tennessee, just south of Nashville. He died the next morning on October 11, 1809. At the time, the shooting was called a suicide, but most people now believe he was murdered (randomly, not as a premeditated target). Jefferson -- for as long as he'd known the man -- admitted that he had suffered from "hypochondriac afflictions."

"Hypochondriac afflictions" is not something you can catch, its a mental disorder. It means that the person has a "health phobia" or constantly has this worry about whether or not they are sick or going to be sick. But Lewis was also very moody, introverted, and what people back then called "melancholic". Therefore, he may have also had bi-polar disorder or chronic depression.