RIP My Naso Tang

[The Guy]

Came home to find my Naso tang as the main course for my clean up crew.
Last night he was swimming, active & eating well. All my water parameters are good and everyone else is fine tonight. His only large tank mates are a Yellow and Kole tang, long nose hawk fish, coral beauty all the rest are clowns,damsel,chromis and some bottom fish. Has anyone else had this happen for no apparent reason or should I be overly concerned.