Here's my take on a med bed (don't care what you think, you have your own mind).

The human body is zombified without a functioning central nervous system.

Wouldn't matter how much hormones, stem cells, injections, nanobots are inserted, the body would just lay there.

So, my view.

The CNS pulses energy back and forth (head to toe and fingers and back to head).

The med bed follows this pattern, like a massage for the CNS.

A device that runs up and down the body, stimulates the CNS.

Energy input by the device can be modified as needed.

Similar to an energy field that can be assimilated into the CNS.

A food and drink supplement would have to be taken before, so repair can take place.

TLDR: A device that goes up and down and transfers energy into the CNS.
Our CNS hardly gets a workout now, too dormant.