everything in the universe happens chemically. when things happen chemically their ionic charges change between atoms. ions are an electric charge that can be measured by sensitive magnets when occurring in very small scale, as it happens in the brain.
the brain is a big chemical reaction. it's chemical reactions occur at a certain rate, which causes the ion charges to change across the brain at a certain rate. these ion/charge rates in the brain can be measured by an EEG, which is a system of very sensitive magnets that are attached to the head in different areas.
ion channels in the membranes of neurons regulate the passage or restriction of these electrical impulses through different neurons and cells
when the chemical reaction and ionic charge in the brain happens at a different rate, usually much faster, it is called a seizure. when this happens often the person is considered to have epilepsy.
when an EEG measures normal brain activity there is a standard speed of transmission. when a seizure occurs EEGs usually show a faster rate of charge through the cell membranes than they can handle causing overflow of charge on the outside of neurons, increasing the electrical potential on the outside of the cells, which means it goes somewhere else, and the only other place it goes is to different neurons (I haven't QUITE yet mastered shooting bolts of ionic electrical discharge out through my fingertips

), and when it goes into different neurons, it does things to your brain that "you" don't do.
think of it like a kitchen sink, and the drain is your brain sucking in life experiences, and the water is the ionic impulse of your neural activity (your life experiences). you use the sink day by day at a regular rate, say, 10,000 per second, and you do this with 100,000 sinks (much fewer than you have neurons) at different but nearly the same times. suddenly your sink starts randomly shooting out water 10,000 times faster, and starts making the sinks near it do the same, with the force of a firehose. and it starts doing that randomly. once it happens more than twice, your "plumbing" has epilepsy.
epilepsy drugs try to act as "valves" that try to control the speed of the water coming out. the better your plumbing (health) is overall, the better the "valves" will work.
but so then every so often you get a flooded kitchen. at least it's water and not urine or blood all over the house - lol.
but it's easy to think of a seizure like a "lightning bolt" - I like the sink overflow concept, as that's more like what's happening, because it's flow vs. restriction, and the ability to move that flow through normal channels, lest it makes the sinks overflow into different sinks
but this happens on a cellular level, where each ion channel (there are many in each cell) is its own "kitchen sink", with sinks abutted up to each other as far as you can see. when ONE sink gets the "mega firehose", often it causes smaller seizures (absence seizures and things where consciousness is preserved) but doesn't really disrupt the on/off or cause much overflow the individual sink can't handle on its own within a few moments (absence seizures etc) or that the adjoining sinks can't handle (larger seizures).
when larger expanses of the sinks get "the firehose" at once it causes larger overflows that spread to more and more and more sinks. this type would cause larger, longer and more severe seizures (ex. tonic-clonics (the unconscious shaking type))
in this very very very simplified "kitchen sink" example, think of each sink performing a different thing. one sink makes you walk. one sink makes you pee. one sink makes you love. one sink makes you scream. one sink makes you remember a moment in high school. now have all of these sinks overflow into one another whereas usually each has its own plumbing path. that's why some crazy shit goes on with epilepsy.
different parts of the brain are associated with different aspects: memory, good feelings, bad feelings, sensory, yadda yadda yadda -
obviously this is a disrespectfully ridiculous description of the brain and its functioning, but this might give you an idea.
don't think of seizures like lightning or a "tazer".
think of a kitchen sink for every millisecond of your life, a sink that persists or dies, and the sinks keep piling up and up. each sink associates with every emotion at that millisecond (leaving a stain around the drain - lol) and every millisecond thereafter until its demise, and builds itself plumbing to associate with each area of the brain (memory, good feelings, bad feelings, sensory, yadda yadda yadda -). and then starts turning on and off on and off, 10,000/sec,...