Sialorrhea is a symptom of the disease where a person experiences drooling and excessive saliva. While some physicians think that this is a motor symptom, some believe that it may likely be the result of dysphagia and other problems with swallowing. Likewise, other automatic movements of the body may cause it as well. 

If you’re suffering from Parkinson’s, you’ll see these automatic actions declining. Also, the amount of saliva you’re producing may be normal but you’ll find it difficult to swallow, which causes you to drool. Basically, the more extreme the drooling is, the harder it will be to swallow.