Hello! Welcome and thank you for asking on HCM! I understand your concern and would explain that your symptoms may be related to the raised sinus pressure from the nasal obstruction. The fact that your headache is relieved by Exedrin and sudafed is another argument in favor of this cause. From the other hand, antihistamines can cause these symptoms (slow thinking and sleepiness) as a common adverse effect. Do you have these symptoms when you don t use antihistamines? What type of antihistamines are you taking? I recommend you to consult with your allergologist and try to find another therapy for hay fever (immunotherapy or a non sedating histamine). Caffeine (in the coffee) could also be helpful if you tolerate it well. Hope to have been helpful! Best wishes! Dr. Aida