Honestly, I have no idea why Djokovic does the strange things that he does. I can only imagine that it serves as some sort of motivation to help him get locked in, especially for a match where it is easy to be flat. But I know that I've never seen another top athlete from another sport do the sorts of things that he does. If he's not outright pretending to have a significant injury, he's feigning to be on the edge of exhaustion or collapse.
And as I already said, I've played plenty of sports, and I've even been paid to play one of them (label that as you like), so I'm very familiar with various forms of injury. The things you call a "bother," that you can play on with, don't come on in dramatic fashion. Those are really minor things. Anything more serious, and perhaps you can continue at less than 100%, but your limitation would be consistent (as in, you would be less than 100% throughout, not just a certain times or on certain points). But, more importantly, there are some significant injuries that you simply cannot play with. Nobody is sprinting flat out with a large hamstring tear. It just doesn't happen on this planet.