ashamed, painful, guilty conscience
疚 centers on a painful inner state of guilt or shame: feeling ashamed, having a guilty conscience, or experiencing emotional pain from wrongdoing.
疚 combines 疒 (sickness) with 久, which likely contributes the sound. The idea is a sickness of the heart or conscience, leading to shame or guilt.
The sickness enclosure 疒 wraps around 久, like a long-lasting illness of the heart. Picture a guilty conscience as a chronic pain that makes you feel ashamed.
For キュウ, imagine a guilty person feeling like they are in a queue for punishment: queue -> キュウ, and the shame makes them feel sick inside.
feeling guilty; having a guilty conscience; having qualms about
I have nothing to be ashamed of; I have a clean conscience