rush, hurry, be flustered
忩 centers on a state of hurried agitation: rushing, being flustered, or acting in a frantic hurry.
忩 combines 公 (public) and 心 (heart/mind), likely suggesting a mind that is publicly agitated or hurried. The exact historical development is uncertain.
The top 公 looks like a person rushing about in public, and the bottom 心 is the heart. Imagine your heart racing when you are flustered and in a hurry in front of others.
For ソウ, picture a flustered person rushing to sew a torn garment in public: sew -> ソウ, and the hurried sewing matches the kanji's meaning.