I agree, chances are it may be your bedding you are using so change the bedding and see how it works.
If it does get worse though, you'll really need to go to a vet; its common for rats to have some inactive virus that will lead to RIs whenever it is activated (sorry i cant think of a better word to use lol). My rat came down with this and he was very lethargic, wheezing, and obviously ill. we took him to a vet and he got some medicine to put in a vaporizer if he has an attack and another oral medication. 2 weeks of treatment later and he was back to his fat and cheerful self.
I'm sure yours is fine, but he got to his condition very quickly and the vet said that he may not have made it if we didn't take him to the vet when we did. SO if your rat does get worse please seek medical help, they may be able to work with you on payment options.