Acetylene used to be used as a general anesthetic, it is much more potent then tradition nitrous oxide. It was discontinued because the reaction with oxygen is dangerous. It can, like anything be deadly in large dosages, and impurities in it are usually the more toxic effect. But the prolonged dizziness is perfectly reasonable, being it a very strong anesthetic. Obviously if it continues the next day or you notice any other problems go see a doctor immediately (such as trouble breathing, constant continuous headache, fever, etc). But I would not worry at all if all the effects are gone.