My Dog Gags All The Time When He Lays Down What's Wrong?

Your dog is gagging because he tries to clear his throat. Excessive mucous production in dogs can cause irritation and problems with the pharynx. Following are reasons of excessive mucous production.

1. Bacterial or viral infection
2. Anatomical abnormalities
3. Allergies
4. Tonsillitis

So, you should take your dog to vet for differential diagnosis and treatment because treatment depends upon underlying cause.