Is it possible to have pneumonia or bronchitis without having fever or having a cold/flu first?

Absolutely. You can have pneumonia or bronchitis, and the first symptoms you have are the symptoms of the pneumonia or bronchitis. Nothing else has to happen first.

Related Questions

Could you potentially have pneumonia or bronchitis without a fever or having a cold/flu first?

See below. What you are asking is whether the pneumonia can develop without earlier symptoms and the answer is yes it can suddenly happen.