On the television show Fear the Walking Dead, one of the main characters is a heroin addict. After a couple of days without heroin, he goes into intense withdrawal, and either has a grand mal seizure or pretends to. His family is used to his addiction, and when his mother returns home from an errand, his sister says, rather matter-of-factly, "He went grand mal".
According to this website, heroin withdrawal alone doesn't cause seizures:
Heroin withdrawal on its own does not produce seizures, heart attacks, strokes, or delirium tremens.
So why would a person in this situation have a seizure? Is it more likely to be the result of his sudden withdrawal (contradicting the quote above), or is it more likely to be a side effect of the use of heroin itself, or is it more likely that he has a medical condition that causes seizures, but which is totally unrelated to his addiction?