If your Eustachian tube is blocked your eardrum cannot vibrate naturally so sounds may seem to be muffled or blocked. Eustachian blockage is experienced during flying and tinnitus may appear to get louder temporarily. It is best to continue your medications and take nasal decongestants and antihistamines as advised. Do consult your ENT specialist and clarify your doubts before travelling by air. Do keep me posted on how you are doing.
Best luck and regards!