Normally, all mucus secretions from the nose drain to the back of the throat and are swallowed in a process we're not usually aware of. However, sometimes a person may feel as if mucus is accumulating at the back of their throat. This is termed 'post-nasal drip'.
A person may describe this as a feeling of mucus dripping or trickling down the back of their throat, which may trigger coughing. Post-nasal drip may occur when a person is suffering from a cold or an allergy.