Epilepsy

It depends on the circumstances. You cannot, as a general matter, be fired simply for having a medical condition like epilepsy, but you can be terminated if:
1) You have a job that you just can't do with epilepsy without risk of personal injury and/or property damage: e.g. vehicle driver, equipment operator, a repair person using tools, assembly line worker, warehouse employee (who needs to go up on the high lifts, etc.)--i.e. any job where if you had an attack or fit, you and possibly others could be injured or die, or expensive equipment or property destroyed. The employer is not required to bear those risks.
2) If during a fit or attack on the employer's premises, you did in fact in any way injure another person: the employer would face liability if, after a demonstrated injury to another, it did not take steps to stop that from recurring.
3) If your condition is so severe that rather than occassional attacks or fits (apologies, by the way, if I do not know the correct terminology), you regularly or predictably have them during work hours: that would be highly disruptive to the employer to have this occur commonly, and they are not required to bear that level of disruption to their operations.
4) If it is reasonable that you would have an attack or fit at work, but if you do, the  nature of it is such that you would require more attention or help than it is fair or reasonable for your coworkers to provide--the employer is not required to risk that.
So it's not having epilespy per se that could legally get you fired; but if your elipsy significantly burdens the employer with workplace disruptive or risk of injury or liability, the law does not force them to bear that risk or cost. Therefore, the nature of your condition and what has happened at the workplace due to it determine whether termination over it is legal.