Feel Great Before Bm. After Bm, Extreme Weakness In Legs

Feel great before bm. After bm, extreme weakness in legs and feel tired. After little over an hour feel ok. Have high risk of colon cancer (death of brother, 2 uncle's, cousin, grandfather) and I am on top of keeping up with tests as I keep having the polyps removed each colonoscopy. I also have lower back pain every day due to two buldgeing disks. I have other back and limb issues such as scoliosis, stenosis, pressure palsies and drop feet (HNPP). There are some respiratory issues that I believe are irrelevant to the bm/weakness problem. What is your opinion to the extreme weakness in legs after bm?