Honestly i cant tell you what causes the damage the the muscle.It could be something you eat, it could be anything, Im no doctor im just telling you what i was told. My doctor told me that the muscle can just become weak, or weaker over time, and that laxatives can damage it. Also i dont really suffer from anxeity. Im sad alot, but thats because im sad about the problem. If i find myself in a situation that i smell i may have an anxeity attack, but not like a melt down or anything.
Also the feeling of not finishing a bowel movment and or using alot of toliet paper to clean up after a movement would have a lot to do with the spincter. Googl spincter and look for a picture of the human spincter. The doctor told me that there are two spincters there like little balls i beleive. So if there not open or closing right, inturn there would be stool stuck, or not properly released.