If you can find an after hours emergency vet service, call them.
Does your dog have an appetite? The standard thing to try with dogs is rice and boiled hamburger.
If your dog has no appetitie, can it hold down water? Also, loss of appetite can be a sign of kidney problems.
Has your dog experienced a sudden loss of energy?
If the dog has lost appetite and energy, it could be an infection, and if so the worst case scenario would be if it is leptospirosis (aka āleptoā), which is something my late cocker spaniel Roscoe had about 6 years ago and is a deadly bacterial infection of the kidney and must be acted uopn quickly (if I had not been able to get him in to the vet on the day I did, I suspect he would have been gone in a week).
When you take the dog to the vet, ask for a lepto test. It ran me about $90 with Roscoe, but it can get to the heart of the matter quickly (and save $$$ on other tests) or rule it out. In the meantime, until then, you should get a spray bottle and fill it with a bleach-water solution and spray wherever your dog urinates, since that is one the more common ways of transmitting it.
In the end, I pray that it is not the worst case scenario. But please let us know what transpires. In the meantime, may St. Francis interecede to our Lord for your intentions.