The nasal block could be due to a sinus infection, a cold or a chronic allergy. It could also be due to a deviated
nasal septum or
nasal polyps. Sinus infection causes blockage of flow especially when a person lies down. The blockade is affected by the side to which the person turns also. You will need to consult your primary care physician for proper assessment. In the meantime practice good breathing exercises, humidify your room and do steam inhalations.