What triggers seizures ?

Many conditions : many conditions can trigger a seizure. There usually needs to be a scar on the brain at your age group. Infection, lack of sleep and skipping meals can lower the seizure threshold enough to trigger a seizure.

LACK OF INHIBITION: The brain functions in a homeostatic balance with both excitatory and inhibitory neurotransmitters in balance. Individual nuclei have an "inhibitory surround" to prevent inadvertent firing. If an abnormal brain lesion blocks normal connections, the inhibition is blunted and excitation pre-dominates, sensitizing a spread of electrical action, which could trigger a seizure.

What doesn't?: Dehydration, use of illicit drugs, infections both at the level of the brain and spinal cord as well as anywhere else in the body medications, flashing lights, noncompliance with anti-seizure medication regimen, strokes, metabolic disorders, trauma to the head, hyperventilation. Does that list seem complete enough to cover whatever you might be thinking? There very well may be other causes as well