James Caan -- Out Of Misery, Back to Work (PHOTO)

James Caan wasted no time ... less than 48 hours after he went to an emergency room, he was back at work, and smiling with his co-star Louis Gossett Jr.

TMZ broke the story ... the 75-year-old showed up to a Toronto hospital Tuesday night for a mild chest infection. He was treated and released, but we were told he'd be unable to return to set for a few days. No rest for the wicked.

Caan and LGJ are filming the family comedy "From Here to Infirmity."

Sweet irony.