I suggest calling the veterinary hospital and explain the symptoms to try to get a good diagnosis. If you go in right away, you may have a co-pay or whatever it's called in veterinary practice. You will probably have to bring him in anyways.
You could have a point with that idea, but considering that your dog is acting similar to a rabid animal, it would be a good idea to avoid contact with any of your dog's fluids. Use extreme caution in cleaning up the vomit if this is the case—though it seems unlikely.
» And then I realized it was night. Not sure if you can get in touch with the vets at this hour.