Hi there.
The first thing you should do is to backup any important data which you might have on that drive as soon as possible, just to be on the safe side. After that I'd suggest that you download the HDD manufacturer's diagnostic tool (or a 3rd party diagnostic tool if you don't know the manufacturer) and run the tests to see what's the situation with the HDD.
Some other things you could try is to connect it to a different SATA port with different cables, or even better - to try it with a different computer, to see if the same issues occur.
Hope that helps. Please let me know how it goes.
Boogieman_WD