NEW YORK — David Letterman is thanking Rhode Island hospital for making the best out of a “scary” situation. The former “Late Show” host, 74, revealed that he hit his head on the sidewalk last August after he tripped while walking in Providence with son Harry, then 17. “I go unconscious — never been knocked out before in my life,” said the “My Next Guest Needs No Introduction” host in a video published Thursday. Letterman said that passersby called the paramedics and he was transported to Rhode Island Hospital. “They stitch me up, they X-rayed my head. They gave me a CT scan, they scrubbed me …