Gastroesophageal reflux disease (GERD): This is often considered the most common cause of hiccups due to the irritation of the nerves that control breathing, which can be triggered by stomach acid flowing up into the esophagus.

Eating too quickly or drinking too much: Swallowing air can irritate the nerves that control breathing, leading to hiccups.
Spicy or sour foods: Irritation of the nerves in the stomach can cause hiccups.
Stress or excitement: Emotional states can sometimes trigger hiccups, possibly due to changes in breathing patterns.
Alcohol consumption: Similar to eating too quickly, drinking alcohol can lead to swallowing air and irritating the nerves.

Pneumonia or other lung infections: Infections in the lungs can irritate the nerves that control breathing, leading to hiccups. Missing a lung infection could lead to severe complications.
Pulmonary embolism: A blockage in one of the arteries in the lungs can cause sudden onset of hiccups among other symptoms, and is a medical emergency.
Cardiac conditions: Certain heart conditions can lead to hiccups, either through direct irritation of nerves or through changes in blood flow and pressure.
Neurological conditions: Conditions affecting the brain or nerves, such as stroke, meningitis, or multiple sclerosis, can cause hiccups and are critical not to miss.

Laryngitis: Inflammation of the larynx (voice box) can lead to hiccups, though this is less common.
Gastric dilation or volvulus: Conditions where the stomach becomes distended or twisted can irritate the nerves and cause hiccups.
Surgical complications: Post-operative hiccups can occur due to anesthesia or surgical irritation of the nerves.
Metabolic disorders: Certain metabolic conditions, such as diabetes or electrolyte imbalances, can lead to hiccups, though these are less common causes.