Seeing the look in her eyes, my heart was filled with remorse.
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usage
In modern Chinese 疚 means guilt, almost always in 内疚 (inner guilt) or 愧疚 (ashamed and guilty). The original chronic-illness sense is now rare and literary.
The sickness radical, a person reclining on a bed. Guilt is framed here as a sickness of the heart, a gnawing inner ailment, which is how the illness radical ended up on an emotion word.