My jack Russell has lost feelings in his legs

I have a jack Russell terrier that is 13 years old. On Wednesday night at 9:30pm he lost control of his back legs and just couldn't walk anymore. Before this he was walking fine and had no issues. On Thursday morning I took him to my local vet, they did a thorough consultation on him. Feeling his spine and legs. He did not flinch at all. I don't know if this shows no pain? They then suggested a x-Ray. They xray from the vets point of view showed a healthy spine. Then a xray specialist on site had a look and suspected something on the L4 and L5. But said take him home and give him 5 days cage rest with metacam and we can then reassess. Since Thursday he hasn't had an bowel movement. His front legs have gone weaker. He refuses and probably just can't walk. He will let me know if he is thirsty or needs to pee. He will stand with my support to pee for that 10 seconds and then he just collapses.

I am really confused with what's happening and unsure what to do. I've had him since he was born and I just can't bear seeing him like this.

If you can shed any light on this, it will be very greatly appreciated.

Thankyou Amy