They started late one night, the tremors that shook Michael Harding’s whole body when he lay down to sleep. “A bit weird,” thought Harding, then a 23-year-old Australian soldier stationed in Afghanistan. Just days before, he’d been in an hours-long siege in which his second-in-command was shot and killed.

Harding soon started shaking so much that he had to ask a friend to light his cigarettes. He couldn’t drink water from a bottle without pouring it down his shirt, and in the mess hall, his twitches got so spastic that he’d sometimes flip his tray.