Hello, and thanks for writing in.
Nutmeg can potentially cause toxic effects in dogs. Nutmeg contains chemicals that can cause severe hallucinations and signs including fast heart rate, and skin flushing. A small amount of nutmeg in baked goods is probably not going to be a problem but eating a large quantity of baked goods or eating straight nutmeg could be a problem.
I would rinse the mouth out well with water. If your dog is showing abnormal symptoms, the best medical advice I can give you would be to have him evaluated by a veterinarian so they can determine if further treatment is needed, such as IV fluids or specific medications. It's possible that the symptoms may go away on their own during the day, but if you elect to watch him closely and the symptoms are persisting, I would recommend that you get him into a veterinary clinic today if at all possible.