Should I be worried about pneumonia in my cat?

I have two cats and for a week they were sneezing and had clear nasal discharge so I waited because I suspected it was an upper respiratory infection and needed to resolve itself. That was almost 2 weeks ago and one of my cats he coughed twice within those two weeks. And I got paranoid and now i'm obsessed with watching his breathing because i'm scared he got pneumonia. He keeps smelling things and when he smells I can hear him smelling (never used to). And whenever he sits he sits like a coughing cat (not sure how to explain that - anybody who has a cat with asthma knows what i'm talking about) My question is for those who have had a cat develop pneumonia, especially after a URI, do they act sick or normal? Are the symptoms very noticable. My cat eats normal, drinks, and plays but he did cough, and his breathing is different since the URI. I am the type of person who worries to much and I waste alot of time and money going to doctors for my cats or even myself because I think they have something serious and its usually nothing. So thats why i'm asking, to learn how other peoples cats acted when they had pneumonia so I can stop worrying or bring him to a vet.