qualm

This term describes a sharp, sudden prick of conscience or a momentary lapse in confidence regarding the morality of an action. It is most frequently encountered in the negative, such as in the phrase "without qualms," to indicate a complete lack of guilt or hesitation when performing something questionable.

In a physiological sense, the word refers to a brief episode of nausea or dizziness. While this physical meaning is less common in modern daily speech than the psychological one, it retains a sense of suddenness and instability, mirroring the mental "shiver" of a moral misgiving.