Answer:
The Hmong believe that an epileptic seizure is caused by a malicious spirit called a "dab", who possesses the body of the epileptic patient and causes the event. The dab take hold of the patient's sould and the epilepsy is a result of that.
Some Hmong become Shamans in order to help communities with demonic possessions. When they find an epileptic patient, they perform rituals, and provide traditional medicine to deal with the problem.
It is important to highlight however, that the Hmong are becoming more educated in Western medicine, and many of them, especially young people, now understand epileptic seizueres as neurological problem.