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Since he is not able to hold water down, I recommend having him looked at today if you can get in. Your vet may be able to get you in for a same day appointment so I recommend calling and letting them know what is going on with your dog and see if they will be accommodate a same day appointment. If your vet is not able to get you in, your next option would be to go to an emergency vet for evaluation. Some places are open 24 hours and will be able to see your dog during the day but others are only open after hours, when general practitioners are closed. If they are unable to see your dog today, your veterinarian's office can recommend an alternative.
Let me know if you have any further questions or concerns.