If you are guilt-ridden, the guilty feeling is so strong that it sits on you and will not get off. You cannot park it to one side and think about other things; it keeps coming back. The second half, -ridden, is the same piece you meet in bedridden or debt-ridden: it paints a picture of being ridden, as a horse is ridden, by something that has you. The word is stronger than plain guilty. A person can feel a little guilty and still laugh at dinner; a guilt-ridden person is stuck inside the feeling. Writers like it because it is dramatic. In careful talk it describes people, faces, silence, even a whole country in political writing — though actually that last use is a stretch, a metaphor, not a courtroom claim. It is usually hyphenated: guilt-ridden.