It sounds like he had a seizure. There isn't anything you can do for him during this unless your vet has prescribed something to give.
There is a medication to give that will help stop the seizures should this become a problem.
If he has another one, I recommend seeing a Vet shortly afterwards so that bloodwork can be run to rule out any internal diseases such as kidney or liver disease. He may also have an IV catheter placed and the vet may want to watch him for the day to see if he has another.
Sugar water is good for diabetics who's sugar has gotten low and they have become weak.
Older dogs can develop epilepsy and will be prescribed medication to be given on a daily basis to control seizures. Usually this will only be done if the seizures are happening frequently such as once a week.
For now, you may want to jot down the date and how long the seizure lasted for future use in case it does happen again and you will be able to tell your vet this info.
I hope this has helped.
Thank you
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Always consult the advice of your veterinarian if you are in doubt.
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