no, mine did it and a month later he was back to normal, I think the only thing you need to is to is to leave him in the same place without disturbing him.
They periodicaly loose their crowns, I don't know why. Mine have done it before when they were not very healthy and tank parameters were not right. But they always grew a new head shortly after.
Well here it is three weeks later and I just found that the feathers of the feather duster have grown back, albeit smaller that before. For once I just left him alone and all is fine today.
When mine (actually the featherdusters feathers) grew back they were much smaller,
they've now almost grown back to the original size, but the feathers are a different colour now ( completly white).
i have heaps of white feather dusters they grow radomly though the sand bed
i also have a nice colony of christmas tree worms that range from blue to greens to yellow there really nice i lost a couple but i see new tiny ones often