Respiratory problems easily rival gastrointestinal diseases as the most common problems in the traveler to Nepal. Pollution in the city, cold air in the mountains, dog hair, and pollen dust could be inciting factors of respiratory disease. Unlike the guidelines for gastrointestinal problems, however, guidelines for respiratory ailments are not clear cut.
Let us start with the classic nagging "Khumbu cough" that disturbs sleep and is common at high altitudes anywhere in Nepal. Breathing cold air probably predisposes you to this cough, which actually may be caused by a virus. Sometimes there may even belong spasms of coughing which leave you breathless. There usually is no significant associated fever. It is best to have a doctor or a nurse check it out if you're lucky enough to find medical personnel in the mountains; however, an antihistamine like Benadryl may work wonders, especially at night, and allow you to sleep more peacefully. Codeine, which also suppresses coughs, I will be deleterious at high altitude.
Sinister causes of cough in the traveler such as tuberculosis are definitely uncommon even in areas where tuberculosis is endemic. Exotic causes of travelers' cough do exist, but they are rare. Better to be concerned about common cough problems and how to avoid keeping your tentmates and lodgements awake at night.