Answer:
Doctors are not clear why hiccups happen but they think it may involve irritation of the nerves or the parts of the brain that control muscles of respiration (including the diaphragm).
Brief episodes of hiccups often have no obvious cause but sometimes are triggered by
A bloated stomach
Alcohol consumption
Swallowing hot or irritating substances
In such cases, hiccups usually start in a social situation, perhaps triggered by some combination of laughing, talking, eating, and drinking (particularly alcohol). Sometimes hot or irritating food or liquids are the cause. Hiccups are more likely to occur when carbon dioxide levels in the blood decrease. Such a decrease can occur when people hyperventilate.
Persistent episodes of hiccups sometimes have more serious causes (see Table: Some Causes and Features of Persistent Hiccups). For example, the diaphragm may become irritated because of pneumonia, chest or stomach surgery, or waste products that accumulate in the blood when the kidneys malfunction (uremia). Rarely, hiccups develop when a brain tumor or stroke interferes with the breathing center in the brain.
When the cause is serious, hiccups tend to persist until the cause is corrected. Hiccups due to a brain tumor or stroke may be very hard to stop and may become exhausting.
