For future reference, I always notate which drive my OS is installed on. If you look at the drives in your BIOS, you can see that they have unique identifiers. I also make a note on the HDD itself with a sharpie. Redundant? Yes, but I'd rather be safe that sorry. I've been in your shoes one too many times. That might help you in your future troubleshooting though. Best of luck to you!