Why would my legs sometimes ache immediately when using a saline enema for consitpation? I do not have high blood pressure?

See below. How often do you use enemas or laxatives for constipation? Too frequent use can lower potassium levels, which can cause leg cramps. Magnesium may similarly be lost & cause cramps. Increasing dietary fiber (& using fiber supplements) with plenty of fluids should keep bms regular. For potassium, eat bananas, kiwi, strawberries; for both minerals: cilantro, beans, sun-dried tomatoes, nuts, etc.
Unusual symptom. The positioning on the commode to instill the enema may unduly place pressure on the back of the thigh resulting in the ache. Straining for the elimination process will do the same. Doubt that the saline has anything to do with the ache, nor will variability in the blood pressure.