This is the kind of advice I was seeking - first-hand reports from paralyzed users of LSD/etc. - not guesswork from a doctor.
I have some leg tremors/writhing when experiencing pain or stretching certain muscle groups. As I understand it, it's due to hyperreflexia in the body which is innervated by parts of the spinal cord below the injury site. The reflex arc is still present and functional, and there is nothing from the brain to inhibit it.
Presumably serotonergic psychedelics would make tremors/writhing more apparent by their activities as general sense-amplifiers, and also because the lower half of my body lacks any sort of inhibitory signals sent by the brain. I guess if I want to approach such drugs I should do so carefully...