That circling spunds like some toxicity or atypical enviromental issues (electrical current?)
Regarding the other fish, the causes of death also sound very unusal, to the point of being unbelieveable. I highly doubt a healthy NAso would "choke" on sand. And crafty reef fish like Yellow tang dont get "Stuck" in the rocks without a rock collapse. I am not saying the events didnt occur, Im just saying theyre not the cuaase of death. All three of the fish exhibiting unbelievable symptoms leads me to definitely conclude there is something diagnostically wrong with the water. As you say there is no real problem in their condition and appearance, I am going to stay with toxicity in the water. Any recent construction/chemicals/activity near the tank? Could something ahve been used in the tank that shouldnt have? I recall a similar story, and the tank owner eveentually found batteries in the sumop that his child had been placing there. I would suggest starting with a significant water change, and run carbon.