expression, godan verb (-mu)
worry about; fret over; be anxious about
Used when someone dwells on a problem or takes something too much to heart, often with a nuance of brooding or excessive worry.
彼は小さな失敗を気に病んでいる。
He is worrying about a small mistake.
あまり気に病まないでください。
Please don't worry too much about it.