Why does holding in poop feel sluggish?

Stool retention: Voluntary stool retention, against a physiologic urge to defecate on a normal schedule, results in rectal and colonic distension, increases colonic mucus secretion, & makes stools harder and more dessicated which in turn may result in straining & a sense of incomplete evacuation when you do defecate. Any of these physiologic responses may give you a sluggish sensation. Try to avoid this behavior.