What Causes Severe Asthma Attacks: Allergies, Exercise, Heartburn, Medications, Weather, Smoking, Sinusitis. During an asthma attack, the airways become inflamed. The muscles around the airways contract and the airways produce extra mucus, which causes the respiratory tract (bronchial tubes) to narrow.

Hypoxemia occurs when blood oxygen levels are lower than before. If the amount of oxygen in the blood is low, your body may not be able to function properly.