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Alcohol or drug abuse
Chronic or short-term congestion of the nose and sinuses
Diabetes, type 1 or type 2, that is treated with insulin (usually)
Drugs that can cause drowsiness
Gastroesophageal reflux Gastroesophageal Reflux Disease (GERD) In gastroesophageal reflux disease, stomach contents, including acid and bile, flow backward from the stomach into the esophagus, causing inflammation in the esophagus and pain in the bottom... read more if severe
Habitual air swallowing
Heart disorders, such as coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more , heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , irregular heart rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more , valve disorders Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more , and congenital heart defects that allow blood to leak from the venous to the arterial system such as atrial septal defects Atrial and Ventricular Septal Defects Atrial and ventricular septal defects are holes in the walls (septa) that separate the heart into the left and right sides. Holes can be present in the walls of the heart between the upper heart... read more
Inguinal hernia Inguinal Hernia An inguinal hernia is a protrusion of a piece of intestine or another abdominal organ through an opening in the abdominal wall in the groin. People have a painless bulge in the groin or scrotum... read more that has not been repaired
Impulsive behavior or being prone to accidents
Lung problems*, such as asthma, lung cysts, COPD, or previous pneumothorax (collapsed lung)
Poor cardiovascular fitness
Seizures Seizure Disorders In seizure disorders, the brain's electrical activity is periodically disturbed, resulting in some degree of temporary brain dysfunction. Many people have unusual sensations just before a seizure... read more
* Possible higher risk of pulmonary (lung) barotrauma.
† Possible higher risk of decompression sickness.