Hello! Drooling or sialorrhea may be a sign of different conditions, from infectious disease to neurologic disorders. Since you say that drooling is during the time that you lay down and is associated with a bad smell, the first thing that goes to my mind is gatroesophageal reflux. Other causes can be oral infections, tonsillitis, mumps, pancreatitis, pharingeal or onsillar abscesses, some liver disease, rabies (if you have been bitten by a dog, rat, bat). Some neurologic conditions like Parkinson s disease, myasthenia gravis, bulbar paralysis, facial nerve palsy, hypoglossal nerve palsy (but other signs, more concerning than drooling should be present to make such diagnoses). Some toxins also can cause excessive saliva production like arsenic, mercury, insecticids etc I hope i have been of help.