Guilt in a dream usually points to something unresolved -- a wrongdoing, real or perceived, that your conscience hasn't let you set down yet. Confessing in the dream can reflect a wish to finally address it directly, while being unable to explain yourself often names how stuck the self-blame still feels.
Mercury conflicts with those who are ruled by Jupiter, and Jupiter conflicts with those ruled by Mercury. - Picatrix (Andalusia, ~1000.AD)