First, an update on troubleshooting I have tried. I refer you to page 2 of this thread for my system specificiations.
1. I have tried the Apple Diagnostics Test that involves holding down the D key before boot time. Reports an all-clear, "no issues found" code.
2. I have tried repairing disk permissions using Disk Utility. Some permisisons related to iBooks were fixed.
3. I have tried verifying the disk using Disk Utility. Disk checks out just fine.
4. I have talked to Apple Care support online. They suggested clearing the SMC and the PRAM. They also suggested working in Safe Mode to see if the problem recurs. I tried the first. The second is unfeasiable since the problem occurs randomly once or twice per week, and I can't afford to be in safe-mode for that long. If anyone is experiencing these very specific types of system freezes (described on page 2 and page 1 of this thread), would you try running only in safe-mode for a week or two? The idea behind using safe mode, the Apple rep described, is to see if it's an Apple software problem or a third-party software problem.
After these steps, I have still experienced a very specific type of freeze (NOT a kernel panic, NOT an instantaneous system-wide unresponsive lock-up) as I described on page two of this discussion, as well as described by russiansergey19.
Reply to Ron P.: I do not have any non-native screensavers installed.
Reply to Kate_Mac: I cannot downgrade from Mavericks, since my computer is a late-2013 Retina Macbook Pro that came with Mavericks pre-installed (cannot downgrade from Mavericks: https://discussions.apple.com/thread/5506824). Besides, since it's a laptop, the extra battery life from Mavericks is very useful. See page two of this discussion for my system specs.
If the problem persists, the next step will be to borrow a temporary computer from a friend in order to enable me to bring my laptop to the Genius Bar for repair.