Hello, I can understand your concern. Hiccup occurs when diaphragm, a curtain like muscle that separates chest from abdomen contracts suddenly. Due to this contraction, you try to breath in air faster. But glottis, an opening between vocal cords, stops this incoming air producing hiccup sounds. There are many reasons that can cause hiccups like emotional stress, gastrointestinal problems, spicy food, hot frizzy drinks, suddenly having hot food after cold or vise versa causing sudden temperature change etc. If you have one of these causes during your flight, you may experience hiccups. If it does not stop, you may have to visit a physician for further investigations to find the underlying cause. I hope this information satisfies your curiosity. Thank you for choosing HCM. Take care. Best, Dr. Viraj Shah