Some Patients may never experience any pain due to an infected tooth. Some may experience pain which may go away on its own or with the help of antibiotics. Just because the pain has stopped does not mean that the tooth is no longer infected.
Infection will be present, but your body has learnt to accommodate the same. Leaving the infection as such without an effective and proper treatment is not recommended as the infection can potentially spread.
The tooth has to be examined with radiographs and clinical findings. Root canal treatment is designed to disinfect the tooth and stop the spread of the infection.