Guilt is a useful emotion with a precise function: it signals that I have done something affecting someone and orients me toward repair. Once repair is made, it fades. That is the complete cycle.
Chronic guilt is something else. It attaches to no act and does not respond to repair, because its message is not “I did something bad” but “I am some kind of bad person” — which no action can repair. It is closer to shame than to guilt proper, and confusing the two is why so many people do more and more and feel exactly the same.
Three frequent sources. Impossible internalised standards: if the internal rule is that you must be available to anyone at any time, any rest produces guilt. Excessive responsibility: taking on accountability for states you do not control — a parent's mood, the atmosphere in a house, someone else's happiness — a common pattern in children who had an unpredictable adult. Depression, in which excessive guilt is a symptom proper, listed in the diagnostic criteria.
A useful test: ask someone to name exactly what you did. If there is no concrete answer, it is not guilt — it is something else wearing its name.