It is a normal physiologic process for the nasal tissue (mucosa) and turbinates to swell when you lay down due to gravity. If you have a deviated septum and/or enlarged nasal turbinates to begin with, there will be less room for this swelling to occur, resulting in increased obstruction or congestion of your nose. If you have underlying seasonal allergies or chronic rhinosinusitis, you may benefit from a nasal steroid spray, which helps control the amount of swelling in your nose. Afrin is a topical decongestant and works to immediately shrink the nasal lining tissue, however, there is high addiction potential with this medication and you risk problems with rebound swelling if you use it chronically. However, the fact that you have some improvement with Afrin does suggest that there is some baseline level of swelling in your nose. Surgery to address the septum and turbinates will help correct the structural issues that would narrow your nasal airway, but will not directly address the underlying cause of mucosal inflammation and swelling (allergies, irritants, etc). Good luck!
A thorough internal examination of the nose, a patient history, a CAT scan of the sinuses and medical management first for nasal obstruction are all required before undergoing surgical manipulation of the septum and turbinates.