Thanks everyone, I found the culprit. It was Rollback Rx as I had suspected. For those who are interested to know why and how this happened, read on.
Firstly, I should mention that till this incident occured, I greatly enjoyed using Rollback Rx. I tried FD-ISR, which had some trouble working well on my machine, but Rollback had none of that. Snapshots took up little space and rolling back operations were perfect, it was literally like going back in time before that problem happened. Blows System Restore away.
Problem: Incremental snapshots are supposed to save space by only tracking the parts that have changed on the drive, so being more space efficient in theory. The problem is that Rollback seems to track every change since the last snapshot. There is a way to exclude certain folders, which I used, but still found myself with huge snapshots. The following threads explain in further detail:
1. Rollback Rx Eats Space
2. Rollback Rx Eats Space again
3. Why is my snapshot so big?
In addition, while the threads linked to above and the official FAQ state that deleting a snapshot will recover the space, I found that deleting a 16,000 MB unlocked snapshot did nothing to free my space as claimed.
Solution: The problem was finally solved when I uninstalled Rollback Rx for good. The uninstall happens quickly in Windows, but the immediately subsequent reboot after that uninstall takes over 20 minutes while Rollback erases itself and the snapshots for good. Further reboots are okay.
Conclusion: Despite the powerful features of Rollback, I feel that its too difficult for me to understand and fine tune to my needs. On the other hand, using Rollback has convinced me of the power of Drive Imaging. Its been a life saver for corrupted installs and those driver issues when trying to install and uninstall hardware. I will continue to use Drive Imaging, but will probably try out another program like what's suggested in the DC Backup Guide