Didn't the bullet (or the shock wave caused by it) nick a transverse process in JFK's lower neck?
A 2000 fps bullet is supersonic in air but not in the body. The speed of sound in the body is about 5000 fps so it subsonic. This means that there is no shock wave, just an acoustic wave propagating rapidly away from the bullet. A shock wave carries much more energy than an acoustic wave. A shock wave has a sudden pressure jump, moves faster than sound, and carries a huge amount of energy that can destroy things. An acoustic wave produces much lower pressure and energy.
The notion that the bullet passing near the spine would cause not only a neurological reaction but a specific neurological reaction that results after several days in a person whose spinal cord was severed was not advanced by any neurologist. It was advanced by someone years later who has no qualifications as a neurologist: Dr. Lattimer, a urologist. Being two letters short doesn’t make one almost a neurologist.