My 42 y.o. son experienced sudden onset lower parapalegia that resolved after 24 hrs. he now has u-shaped marks on buttocks, pain and numbness in leg ?

Disconcerting: This needs a thorough and immediate evaluation, as could be due to problems with blood vessel flow, pathology in the spinal cord or lumbar stenosis, and cannot exclude inflammatory problems. See a neurologist or a neurosurgeon asap. This is not something for watchful waiting.

Urgent: I suggest getting a spine MRI asap and seeing a physician. Causes range from a TIA from the brain to spinal disease. It could be an acute compression of the spine or from vascular injury or cancer. It could be infectious. But it is a warning and needs urgent work up.