Dear McMadre: Chest pain can occur for a number of reasons – some as simple as a gas bubble or pulled muscle to a serious heart problem. A 5 mm spot, in most cases, would be unlikely to cause pain. Since the pain is new and has not resolved, the right thing to do is have it evaluated. As it was the weekend, the ER would have been the best choice.
This particular forum is not answered by the specialist breast nurse at weekends. Personally, I would go to the ER and have your breathing checked out. Better be safe than sorry.