Hello, I really appreciate your concern. Inhalation of certain fumes or chemicals can cause palpitation. I would like to ask you to what chemical you were exposed at that time. Inhalation for 4 hours can cause acute rise in heart rate but it cannot exert chronic effects like you are mentioning. Atrial fibrillation is itself a cause of palpitation. But acute exposure to fumes do not cause atrial fibrillation. So there is nothing to worry about the incident. I advise you to avoid stress of that incident and forget it completely. Anxiety or fear can be the cause of your palpitations. Try some relaxation exercies like yoga and meditation. Hope my answer has solved your query. Take Care. Thank you.