Can having a stuffy nose and postnasal drip cause dry mouth at all? also, why does it seem as though the postnasal drip is worse at night, even when i'm not laying down?

Post nasal drip can be caused by different conditions like sinusitis ,and hay fever ,and dry mouth can be associated with silent acid reflux . Washing out the nasal passages with saline spray can help if used sparingly. However ,if the underlying problem is not corrected , you may continue to have symptoms , so it is advisable to get an ENT evaluation to diagnose the cause of the post nasal drip.