What would cause a seizure if a person has no seizure related ailment?

There are numerous triggers. Here's a partial list:
Electrolyte imbalance; low blood sugar; overdoses of or withdrawal from certain prescription drugs; street drugs like cocaine, heroine, amphetamines and PCP; alcohol withdrawal; infections; and tumors. Young children can get seizures when they have high temperatures.

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Answer:
It could be anything from epilepsy that isn't yet diagnosed, head injury, pneumonia, drugs, or illness.

If a person has a seizure and they don't know what's caused it, they need to see a doctor to get accurately diagnosed and treated.

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Answer:
This kid at my school had a seizure today. He doesn't have epilepsy or anything, it was his first seizure. They think it's because he was exhausted.

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Answer:
Dehydration