Nocebo, more precisely.

I wonder how many of the symptoms are real and are causing suffering of innocents caught in what's now a political tug-of-war.

What does the derailment have to do with politics? (serious question, I don't follow news or politics)

Well the president just told rail workers they couldn't strike like a month ago. They wanted to strike because of unsafe working conditions and skeleton crews and crazy shifts. But I'm not really sure it's a political issue, both parties are on the side of the railroad owners here.

https://www.cnbc.com/2022/12/02/biden-signs-bill-averting-ra...

It's definitely a political issue, but there's no party tugging on the side of safety for railroad workers.

This is the result of deregulation by both parties, and corporate greed cutting costs on safety margins in order to make more profits.

Or are acute injury resulting from exposure that happened at the time of the derailment.

Yes, you're naturally going to see a mix of mass psychogenic illness and actually-chemically-induced symptoms, and it's going to be terribly difficult to tell them apart, especially from just news reports. :-/

Or pre-existing conditions due to chronic lack of health care, if the region is as poor as is described in this thread.

That are worsened by the amount of stress this event likely caused