Once you sit on the toilet and your legs go numb, there are generally two possibilities: the first one is due to pressure on the sciatic nerve; the second one is the presence of a herniated disc. For the first case, because the sciatic nerve travels on the back side of the thigh, so the nerve will be part of the pressure when using the toilet, if the time is longer will affect the blood supply of the nerve, so there will be nerve numbness, that is, the performance of the two legs numb, this situation can be alleviated by standing or reducing the time to sit on the toilet. Another situation is that there is a herniated lumbar disc, if you sit on the toilet, the herniated disc will be aggravated because of the body posture, so it causes numbness in the legs. In this case, you should consult an orthopedic doctor and have a lumbar spine MRI as soon as possible to clarify the nature of the disease.