Friend, when a dog losses the ability to walk acutely this can be caused by many different medical conditions. The immediate concern is that he could have a bulging disc putting pressure on the spinal cord, this would be an emergency; the longer he goes untreated the less likely he will recover. Could there be other causes? Yes, he may just be reluctant to walk because he is weak or ill secondary to a systemic disease, ingestion of a foreign body, etc. to name a few causes.
Unfortunately in this case we are very limited as to what you can do at home. There is nothing I can recommend for you to give at home that will have a significant therapeutic benefit in this case, I am sorry. I would strongly recommend having him checked by nearest ER veterinarian, I would not wait if this was my dog. Besides a hands on examination he will need some testing like xrays and blood work to determine the exact underlying cause. Treatment will be based on exam and test results.
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