Thanks for writing to H.C.M. for your query.
I have gone through your query regarding mouth breating, getting up during sleep to drink water,you are already suffering from hypertension
Since your C.T.scan revailes only minimal mucosal thikening in left maxillary sinus while other sinuses are normal, and adenoid is also not much enlarged, therefore nose and nasal cavity
is not responsible for mouth breathing
I am suspecting that you have a thick and heavy soft palate which is lax enough to obstruct the nasopharyngeal isthmus by falling back ,when you lye down on bed. I hope you are having snoring
also, if so than your sleep gets disturbe due to apnoea.
It will be better to confirm it by sleep study. So please go for sleep study and after that one can decide for your treatment.