There is no causal relationship between sleeping on your back at night and having a cough. There are many reasons for snotty cough, such as upper respiratory tract infections, allergic rhinitis and so on. 1. Upper respiratory tract infections: mostly caused by viral infections, mostly self-healing. It can cause cough, nasal congestion, runny nose and other adverse symptoms. Generally, there is no need to use antiviral drugs, and symptomatic treatment is the mainstay. 2. Allergic rhinitis: when allergic to certain things can cause the phenomenon of runny nose and cough, such as dust mites, pollen, animal fur, etc., should be away from the allergens, if necessary, the use of loratadine and other drugs anti-allergy treatment. There are many reasons for snot and cough, it is recommended to go to the hospital in time, clear cause, under the guidance of the doctor for treatment, usually can take the side position, flat position to sleep, so as not to nasal secretions due to gravity outflow.