The likelihood that someone compromised your system just to rename your bookmarks is approximately epsilon. The most likely explanation is that you did it and

The likelihood that someone compromised your system just to rename your bookmarks is approximately epsilon. The most likely explanation is that you did it and have no memory of it; this can be caused by taking certain sleep medications, having a sleep disorder, or by other environmental conditions (like a CO leak, already mentioned). The next most likely is that a friend or family member with a bizarre sense of humor is playing a prank on you. It is more likely that you own a cat, who is literate and can operate a computer, than that your system was remotely compromised for the purposes of renaming your bookmarks.