In looking at this video, I'm not thinking that this is UNWD, so that's good.
Gas can build up in fish in two locations - the stomach (due to bacteria) or the swim bladder (due to bacteria or pressure changes). One way to try and diagnose this, is if you see the fish stop swimming for a bit (rare in wrasse, I know) the fish will bob up just a bit.
Curing these issues can be difficult as they are internal.
For stomach gas, Feeding peas is suggested, but useless for most fish (it was originally developed for Oranda goldfish that have a specific intestinal issue). Really, anything with a lot of fiber in it (like frozen brine shrimp) will help decrease the gut transit time, in turn, reducing the amount of gas the bacteria is producing. Never let deep water marine fish feed from the surface. Genicanthus angelfish for example, when fed at the surface, will swallow air bubbles, causing them to bloat and float.
Swim bladder issues are even tougher to treat. Sometimes, they develop when fish are shipped by air cargo, as the air pressure in the plane's hold is a bit lower. Their swim bladders expand, and then they have issues regulating it later on.
Jay