My husband developed severe, uncontrolled asthma 2 years ago and age 52. his worst symptom is coughing. why does this get worse at night?

Nocturnal cough : The exact reason that asthma is worse during sleep or at night time are not known. Likely explanations include increased exposure to allergens, cooling of the airways, being in a reclining position (reflux, post-nasal drip), and others. Medications such as proton pump inhibitors, anti-histamines, corticosteroids, & singulair (montelukast) may be tried.

Reflux: Unrecognized reflux can trigger asthma symptoms at night.