• Alcohol or drug misuse

• 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

• Fainting spells

• Gastroesophageal reflux if severe

• Habitual air swallowing

• Heart disorders, such as coronary artery disease, heart failure, irregular heart rhythms, valve disorders, and congenital heart defects that allow blood to leak from the venous to the arterial system such as atrial septal defects

• Inguinal hernia that has not been repaired

• Impulsive behavior or being prone to accidents

• Lung problems*, such as asthma, lung cysts, COPD (chronic obstructive pulmonary disease), or previous pneumothorax (collapsed lung)

• Obesity†

• Older age†

• Panic disorder

• Physical disabilities

• Poor cardiovascular fitness

• Pregnancy

• Ruptured eardrum

• Seizures

* Possible higher risk of pulmonary (lung) barotrauma.

† Possible higher risk of decompression sickness.