If your first seizure occurred without any provoking factor, your recurrence (having another seizure) risk depends on various factors such as findings in your work up, brain imaging, EEG, neurological exam, family history, childhood history, developmental history, history of learning disability in the past, etc.
If all of factors mentioned above is negative that means you have a low risk for recurrence. If your EEG or your imaging is abnormal or if you have had two unprovoked seizures with all other factors above were normal puts you at medium risk for recurrence group.
If your EEG and imaging are abnormal or you have had two unprovoked seizures with either EEG or imaging abnormal that means you have a high risk for recurrence.
Your physician should make the decision whether or not to treat you after first seizure based on the risk of recurrence and also the impact of recurrence of a single seizure due to certain conditions such as socio-economic conditions, high risk occupation, risks of injuries due to falls in elderly and in patients on anticoagulation.