Convulsive Seizures

This is a common misconception perpetrated in media that a seizure must be a convulsion (the kind where the person loses complete control of their body). Thus, epileptic characters will always have these seizures. In fact, there are many different types of seizures that have symptoms that go from simply losing consciousness and staring into space for a few seconds to losing control of a single limb but maintaining consciousness, to the full-blown writhing on the ground episodes. This trope probably exists due to Rule of Drama, as well as a concern that the audience won't be able to tell that someone is having a seizure unless they're convulsing. After that original idea has taken hold, The Coconut Effect ensures its continued use.

Film

Both averted and played straight in The Andromeda Strain (1971). During Dr. Leavitt's first epileptic seizure she just sits there dazed. During her second seizure she falls unconscious and starts convulsing.
The disease in Contagion causes victims to seize and die, that being said, most of the time seizing is shown convulsions are involved.
In the film of The Twelve Chairs, the main character twice fakes an epileptic fit by lying on the ground and thrashing his limbs about.
Appears in Control, though it's appropriate as the film's based upon a true story.

Literature

The fourth book of The Sword of Truth has Cara writhing after a mental attack.
he first book of Tad Williams's Otherland series involves a child having a seizure. Someone asks him about some pretty lights and before you can blink, he's on the ground foaming at the mouth.

Live-Action TV

House averts this trope frequently. Both absence seizures and complex partial seizures have been shown.
Averted on The Young and The Restless. Victor Newman, a longtime character, has been diagnosed with temporal lobe epilepsy (which they portray accurately), which produces seizures that involve blackouts and hallucinations over convulsions.
Archie in Hornblower has to deal with these in the first series. This becomes a plot point in the first episode, when he has one at the worst possible time.

Tabletop Games

Shadowrun supplement Man & Machine: Cyberware. If Cerebral Booster bioware is seriously damaged, the person in whom it's implanted will suffer epileptic seizures with convulsions.

Western Animation

In an episode of The Simpsons where the family visits Japan, they happen to see an anime on TV with Epileptic Flashing Lights, an obvious reference to the infamous Pokémon episode. Everyone falls down to the floor and has a seizure, except for Homer. What makes this even more bizarre is that nobody in the family has been portrayed with epilepsy before or after that.
- The episode offended lots of people with epilepsy - not only because of the episode shown causing seizures, but because Homer doesn't have a seizure; he just 'joins in' and he doesn't have a seizure because he's an idiot.