Dennis Quaid says he was so coked out of his mind during the time he was shooting "The Big Easy" back in the '80s ... he was sleeping ONE hour a night in between drug sessions.
Quaid spilled his guts about his cocaine addiction in the '70s and '80s to Newsweek ... calling it his "greatest mistake."
Quaid explained, "I’d wake up, snort a line, and swear I wasn’t going to do it again that day. But then 4 o’clock rolled around, and I’d be right back down the same road like a little squirrel on one of those treadmills."
Quaid says he finally realized the severity of his addiction when his band broke up ... saying, "I kind of realized I was going to be dead in five years if I didn’t change my ways. The next day I was in rehab."
In the end, Quaid says the experience helped him grow as a person -- "If I hadn’t gone through that period, I don’t know if I’d still be acting."