Having seizures puts a huge strain on the body, apart from the fact you could harm yourself or others. The danger really lies in not knowing what type of seizure you are having (if you are having seizures).

sitke mentioned Non Epileptic Seizures. If a person had non epileptic seizures and was being treated for epileptic seizures, the actual treatments could be dangerous as well.

Psychogenic Non Epileptic Seizures

edited to add: from reading more about PNES it appears that comorbidity with conditions such as depression and anxiety and even aggression is quite high. Treating the underlying conditions can help the outcome of the non epileptic seizures.