The singer and guitarist said his jaw was damaged after he fell down a flight of stairs during a drunken night out in 2003 when he was at art college in Glasgow - but he didn't get it checked out until this year.
He said: "I Busted myself up pretty bad. My eye closed over like a beaten boxer and I lost some teeth, which I got replaced.
"Waking up in a hospital bed with only one eye and the worst hangover I ever had is something I wouldn't wish on my worst enemy.
"Because of my previous night's behaviour to the nursing staff, the only thing they wanted was rid of me so there were no head X-Rays taken.
"Let me be clear right now, I am not annoyed with the nurses, I am only ashamed of myself.
"A few years after that incident, my jaw started to get sore and has been a source of pain for years."
'Chasing Cars' singer Gary told how he finally got his jaw looked at this year after the pain became unbearable and he had to get it X-rayed in Los Angeles, where he was working on his solo album 'Tired Portland'.
He added: "It was then that we traced it back to that incident, as it's the only time I landed on my head from a great height."
Gary now has to have a "dental appliance" which he will wear for a number of months while receiving acupuncture treatments for the pain.