What happens if you don't treat a bladder infection?

Untreated bladder infections/UTI can spread and cause kidney damage and other serious problems. The only way to cure a UTI is to take a full course of antibiotics exactly as prescribed. The infection will not go away by itself. If your symptoms were caused by a UTI in the first place, the fact that the symptoms have disappeared does not mean that the infection is gone. You need to see a doctor to find out for sure if you do have a UTI (or if not a UTI, exactly what did cause the symptoms), and to get appropriate treatment.