Well if he's moving and eating he should be fine. But yeah expect him to be a lil slow for the next few days to a week. A 4ft drop for him would basically be like if ya fell off a 2 story house. Least to say ya wouldn't feel like moving around much either.
But yeah turtles are very tough creatures honestly, but very slow to heal. But yeah as long as he's moving around with no problems and eating he should be just fine. If he start dragging any of his legs however I would take him to the vet ASAP.