The funnyman admits he fell into a spiral of self-hatred and began getting high on marijuana brownies every day until Black stepped in.
Opening up about his treatment for the first time, Gass reveals it was Black who "saved me from the abyss" when his behaviour flew "out of control", telling The Sunday Times Magazine, "I went insane last year. I had to be sent away to the loony hatch. Just rehab. I was eating large amounts of marijuana in brownies... Every day... I'd send my assistant to the store. We have stores where you can buy it. It's crazy. I had a desperate need to be Van Gogh or something. Some tremendous artist. Jack's so successful, what's wrong with me, why isn't this working for me? I hated myself."
The troubled star initially rejected Black's attempts to stage an intervention, but the School of Rock star insisted he get help and hired a private jet to fly his pal to a treatment centre in Utah.
Gass adds, "Thank God we went on a private plane. I didn't want any f**king Southwest Airlines passengers capturing it on their phones. Us hugging in the aisle, crying."