Does the drive have an external power source or is it powered via USB? One thing you could try is format the drive and try a new, not used or extra USB cable, and see if it happens again. If your USB cable, or the seating in the HDD, is crapping out, it can cause read errors when the drive spins up, similar to if you were to power off your PC as it is booting up, and corrupting the drive.
Also with the age of the drive, it could finally be reaching its demise, even though if taken care of properly, it should still be running strong.
I had this problem with a 2TB WD Drive, woke up one morning and my external came up with that same message. I was able to recover the data from the drive, did a clean/format and verified I had the latest HDD firmware. Moved all my data back on the drive and a couple days later it happened again. Went through the whole process of recovery/format only to have it happen again so I contacted WD.
Luckily my drive was still under warranty so they sent me a new one, never did find out the cause of it other than what they listed as "faulty hardware"