Friend, when we see a quick onset of back leg weakness or loss of motor function this is usually the result of neuromuscular disorders like: A pinched nerve along the back as a result of a bulging disc, hip disorders, fractures, etc. However, sometimes we can also see weakness of the extremities with systemic diseases. If you are seeing abdominal swelling this will point more toward a systemic disease like: Tumors
, ascites (fluid in the abdomen), etc. So, in this case on history alone it will be very difficult to determine the exact underlying cause. Unfortunately we are very limited as to what you can do at home. I would strongly recommend walking
in with him as an emergency to your vet's office, this should not wait until Wednesday. It is important to rule out abdominal disorders as mentioned above. Plus, if this is related to a pinched nerve it is extremely important to start him on prescription anti inflammatory medication or this could lead to paralysis. I am certain your vet will not be upset in seeing him as an emergency, he/she will understand, this is what we do. Do Not give over the counter pain killers most are toxic
to dogs and will interfere with certain medications your vet may want to use. Please do not forget to rate my answer - I hope you found it to be excellent. If there’s more I can do, please use the reply tab and let me know. It’s my goal to provide you with excellent service." Thank you for your business and I hope to work with you again soon!