The most common causes of night-time only cough are: 1) the reflux of juices from the stomach into the esophagus (swallowing tube) or even up and into the voice box (larynx), 2) an allergic reaction to some allergic substance present in the bedroom and/or bed or 3) post-nasal drip of mucous from the nose or sinuses into the throat. Another possibility would be that the air in the bedroom is very dry and, especially if your wife breathes through her mouth, drying of the mucous membranes of the throat could also cause a dry cough. One more possibility is that she has (cough variant) asthma ( a type characterized by cough rather than wheeze) and, for many persons with asthma, their respiratory problems are worse at night or in some cases, limited to the night-time early morning hours.
I suggest that she check with her doctor about these possible causes of night-time cough.
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