Please explain what happens during an asthma attack.?

Inflammation!! Although an emotional reaction can precipitate bronchospasm, asthma is caused by a chronic inflammation of the airways. This is possibly due to allergy but there are other causes. Increases in inflammation can cause the release of inflammatory mediators that result in bronchospasm with cough, wheeze and shortness of breath.
Abnormal reflex. A woman was allergic to rose pollen. She goes into a room where there is a bowl of roses and has an attack of asthma. Later it was found that the roses were artificial. That means that it is an abnormal reflex initiated by sensitivity of the brain, even with a visual stimulus. High calorie malnutrition can create this situation by making that part of the brain more irritable.