Chronic Post Nasal Drip, Sudden Feeling Of Blocked Nasal Passage, Breathing Difficulty, Light Headedness, Gradually Resolves, No Triggers. Help?

45yr old female, no known previous health issues, chronic post nasal drip . Started to have episodes of sudden feeling of nasal passages closing/inability to breathe through nose; worsens progressively and leads to inability to get enough air even with mouth breathing , progresses to light headedness, can t stand without feeling will pass out, lasts for about 10-15 minutes then slowly resolves on own but takes about another 30 minutes of sitting to be able to then continue with normal activity. Doesn t occur with any known trigger, not associated with activity (can just be sitting and talking and will occur).