Antihistamines have some anticholinergic effects which can be hazardous with DXM, although cetirizine putatively has less anticholinergic effects than some others.
I dont think taking pseudoepehdrine regularly for allergies is wise;if you use this for more than 7-10 days on the trot, on stopping it you will get rebound nasal congestion.
I am paranoid of my brain. It thinks all the time, even when I'm asleep. My thoughts assail me. Murderous lechers they are. Thought is the assassin of thought. Like a man stabbing himself with one hand while the other hand tries to stop the blade. Like an explosion that destroys the detonator. I am paranoid of my brain. It makes me unsettled and ill at ease. Makes me chase my tail, freezes my eyes and shuts me down. Watches me. Eats my head. It destroys me.