Thank you for writing to JustAnswer with your question.
Have you looked into the possiblity that you have gastic reflux? The reason why, is that it can actually cause increased coughing and mucus problems. Additionally it usually is worse when the effected individual lays down -- this is because there is something wrong with the esophageal spincter - the valve that normally shuts offf the stomach from the esophagus. So, when the individual lays down, the gastric juices get into the esophagus. These juices are extremely irritating - they are meant to digest food - and if they flow up into the esophagus are extrememly irritating to the lining, and also may go all the way up to the pharynx - where the trachea flap is (closing off the trachea or "wind pipe" when you eat or swallow) - irritating this area too and causing coughing and other problems such as increased salivation.
One treatment to help prevent this is to get a foam wedge to place between your mattresses to elevate the head of your bed. You may need to prop yourself up on pillows, or if you have a hospital bed or other bed where you can roll the head of the bed up it should help you tremendously. Another method to prevent the reflux when you lie down is to sleep or lay on your left side -- this helps to keep the gastric juices in your stomach as your stomach opening cannot empy into the esophagus easily if you lay on your left side (the stomach is located on the left side with the opening /valve to the esophagus near the middle of the upper abdomen.)
There are many other treatments for this as well, depending on the specifics of your particular case. Medications to decrease acidity may help; in some individuals where weight is an issue in cause the spincter to close incompletely, weight loss is needed; sometimes decreasing the amount ate at each meal and increaseing the meals to 5 per day can help by preventing over-flow out of the stomach. Sometimes certain foods that are less gaseous or spicy may help in some cases.
So, my recommendation is to see your doctor for evaluation of GER (gasto-esophageal reflux). If your doctor agrees he/she may treat you or send you to a GI specialist for investigative testing and treatment. Until that time sleep or nap with the head of the bed up, and you can also try laying on the left side.
I hope this helps. If you have questions or comments please reply.