Since then, he's been doing a lot better. And about three years ago, he started an online campaign to find the guy who saved his life.
His name is Neil Laybourne, and he's 34. He was walking to work when he saw Jonny on the bridge . . . talked to him for about 25 minutes . . . and just kept telling him things would get better.
Over the past three years they've become close friends. And on Sunday, they raised about $40,000 for a mental health charity by running the London MARATHON together.
The charity is called Heads Together. Their goal is to have more people with mental health issues get help, and not try to hide it. Prince William and Kate Middleton are a major part of it, and they're the ones who convinced Jonny and Neil to run.
Jonny says he didn't really prepare enough. And he also lost two family members a few DAYS before the race. So he was struggling.
But Neil helped him through it . . . they ran the whole thing together . . . and they finished in just under five-and-a-half hours.