Pain is felt when the nerves send signals of pain to the brain and the brain reacts by registering those signals.
A herniated disc may result from impact, i.e., falling, being beaten, damage in an automobile accident, picking up a heavy box from the floor in the wrong way, falling off the bed, slipping on a wet floor, etc.
When there is a herniated disc, the discs are not in alignment. Any body movement will cause further compression. Sideways movement will cause sideways compression of the already herniated disc. The disc is out of place, the muscles and nerves around the disc are also out of place. And everybody knows, pressure brings on pain.
By squeezing a 6’7″ 250 lb. man’s neck with your thumb and middle finger, you can bring him down onto the floor. The neck squeeze is extremely painful to him. You, on the other hand, simply squeezed his thick neck a little.