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. He was medically discharged from the army in 2012 with severe PTSD and left with a new personality: withdrawn and unemotional. His sleep suffered, too. He had nightmares and night sweats. To handle his worsening symptoms, Harding tried two kinds of talk therapy, four kinds of medication, and large nightly doses of scotch and Coke. When each of those failed, he turned to yoga, juicing, meditation and medicinal pot. That helped a little, but Harding’s anxiety and muscle spasms still hadn’t abated. Around that time, his wife did what any desperate person would: she started poking around in online forums for something else that may help with his PTSD. She found glowing testimonials for floating, the practice of lying belly-up in a tank filled with warm water so salty you float.