It is not uncommon for dogs to drool or have a slight saliva buildup when they sleep. This can occur because the muscles that control the swallowing reflex tend to relax during sleep, allowing saliva to accumulate in the mouth. However, excessive drooling while sleeping may indicate an underlying health issue, such as a dental problem or an infection in the mouth. If you notice your French Bulldog drooling excessively while sleeping, it is recommended to consult with a veterinarian to rule out any potential health problems.