Solution 1:

The question isn't "How worried should I be?", it's "Can I worry enough?".

Prepare for the worst. If you aren't making backups make them now. Replace the drive and have it checked by someone else. If they confirm what your software is saying then kudos! You just avoided losing a hard drive. If they say it's fine, rejoice! There we no issues and you were scared for nothing.

Either way you win. The only way you lose is if you ignore it, don't backup, and it fails.

Solution 2:

Yeah, if the S.M.A.R.T status says that it failed, you probably don't have much life left in it. It is impossible to tell you how much time you have left. I just know that in my experience... when the drive says its bad... it is not very long before it corrupts data or stops working all together. Sometimes drives fail without a hint in the SMART status. Consider yourself lucky.