Why did Nick have a grand mal seizure?

Question

In the second episode of Fear the Walking Dead, Nick, a heroin addict, has just begun to suffer the effects of withdrawal, when he suddenly appears to have a grand mal seizure. I've done some research and found that heroin withdrawal itself shouldn't cause seizures, although withdrawal from other drugs can lead to seizures.

It is possible that the hospital administered sedatives to Nick, because he was a heroin addict, and because he was raving about cannibalism when he arrived, and had to be restrained. This seems especially likely because Nick doesn't appear to suffer any symptoms of withdrawal until three days after his last dose of heroin, and a day or two after he leaves the hospital (which is pretty unrealistic, but we'll ignore it for now).

It is also possible that Nick faked the grand mal seizure, because he was trying to prevent his sister from leaving the house, due to the growing threat of zombies. He has obviously had seizures in the past, because when their mother returns to the house, Nick's sister says, rather matter-of-factly, "He went grand mal on me".

I asked a question on Health.SE about the correlation between heroin withdrawal and seizures, and the answer was "There shouldn't be any correlation, so either the show is inaccurate, or the character was using other drugs, or he has some sort of medical issues."

I don't think he had time to use other drugs - he was shooting up, fell asleep, woke up, saw a zombie, ran away, got hit by a car, went to the hospital, ran away again, and after spending the night under a bridge, went home, where he promptly went into withdrawal.

The only opportunity he had to take other drugs was in the hospital, and I doubt that they gave him something that would cause seizures.

So why did he have a grand mal seizure?

Answer 1

The word of god is that he was going through a "hardcore withdrawal."

Showrunner Dave Erickson did an interview with Entertainment Weekly where he explained what happened.

I want to ask you about this scene where Alicia is going to go back to her boyfriend’s house and then Nick starts puking and convulsing as if in a seizure so she stays to help him. He later tells his mom “She tried to leave. I stopped her.” So was he faking that seizure or just taking credit for her not leaving?

He was taking credit. I think it’s true to his character. His mom comes back, she’s gone out to get him his fix because she wants to keep him balanced long enough for them to get in their car, and hopefully, make it to the desert and get away from the danger that’s surrounding them.

And I think that particular scene, you know, he’s an addict and he’s selfish and he wants his pills and he wants more, and it comes off of a moment where [Madison] stares him down and he has to do something to gain favor. So it’s a nice character moment, and I think that Frank [Dillane] played it very well. It was him going through sort of hardcore withdrawal and it led to him seizing, and then he tries to exploit that for his own advantage with his mom later on.

Answer 2

Each of your questions is possible.

Yes, the hospital could have given him sedatives depending on the doctor; some will prescribe sedatives, some won't. He also had a saline I.V in at the very least saline can cause a seizure under the right circumstances (maybe not 2 days later however).

He could have faked it. It isn't difficult to fake a seizure and he could have faked them in the past for attention.

There could be a medical reason why he had a seizure, many medical issues can cause seizures.