If internal sata, seems odd that would be connection problem - with that size psu unlikely that a power problem. Did it happen after a reboot or coming back from hibernate or standby. Or just out of the blue?
It is always a GOOD IDEA to have backup - and for sure always have backup of your critical files, etc. Which should be normal operation, not something should be doing because you feel your hdd might die soon. I couldn't hurt to take a backup of files you normally don't if that is the case if you feel something funky with the drive.
But if all the tests show good -- and happened upon boot or return from standby/hibernation it could be just a odd/rare fluke. Here's the thing if it passes all tests from makers tools, and not showing any smart issues then its not going to be possible to rma, etc. So what your not going to use the drive any more? Because of one fluke weirdness? That seems like a shame - if you don't want to use it anymore, you could send it my way
hehehe I will be happy to use the space.
Like I said you should always have critical files backed up anyway.. So its going to be just like any other drive - which any drive could just die tmrw without any warning. You always hope for warning signs, smart notification, etc. But any HDD could just give out any minute so because you have one weird issue with it does not mean its no longer a viable resource for storage.
Make sure you run the FULL LONG test from the makers tools - if that fails then you should be able to return for replacement, if still under warranty.