Originally Posted by rowan

If you're lucky then it's just a bad spot on the platter and it may get over that.

If you're unlucky then it may be something mechanical, eg something has put the servo arm out of alignment and the feedback circuitry can't properly compensate for that.

The best solution would be to go back in time and regularly back up your data , but failing that perhaps look at vendor provided utilities such as Seatools or WD Diagnostics. I don't know about WDD but with Seatools a "long" test will attempt to recover and remap bad sectors. (Note that this feature will probably only work with Seagate drives, so choose the appropriate application for your brand)