"The two main gases are carbon dioxide and sulfer dioxide. "
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The volcanic gases are a plausible theory.
But obviously CO2 doesn't cause paralyis, all everyone on earth would be paralyzed, since the air we breathe has 0.03% CO2
Doesn't sound like sulphur dioxide causes it either.
The major health concerns associated with exposure to high concentrations of sulphur dioxide include effects on breathing, respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease. In the atmosphere, sulphur dioxide mixes with water vapour producing sulphuric acid. This acidic pollution can be transported by wind over many hundreds of miles, and deposited as acid rain.
http://www.doc.mmu.ac.uk/aric/eae/Acid_Rain/Older/Sulphur_Dioxide.html BUT there could be some small amount of other toxic gas, which could attack the nervous system, causing paralysis -- I think the track you are on should be explored, and I hope the investigators are looking into it.