If you have to fly with a stuffy nose or bad cold, you can ask the airport doctor or nurses for help.
Many passengers prefer water-soluble cold remedies, and flight attendants will be happy to bring you a cup of hot water for the purpose. The demand for hot water is always high on Asian flights. I have noticed that it seems to be the custom to finish a meal with a cup of hot water instead of coffee or tea in Asia.
Cabin temperatures are kept rather cool for many reasons, health issues included. I always recommend passengers wear warm clothing and perhaps bring a big scarf or light blanket to wrap themselves in. At high altitudes it's easier to take off items of clothing than to add them.
For those with a mild cough, consideration of other passengers is paramount, as the others can't get away from sniffling and sneezing passengers in a full aeroplane. Japanese passengers often cover their mouth and nose with protective masks, and perhaps these could be used by others as well?
Stay healthy at your destination
Once you have arrived at your destination, common sense together with a good hand-washing regime and food hygiene will keep you healthy and safe. While travelling, I prefer well-cooked foods and avoid ice cubes, un-peeled fruit, and, depending on the area, ice cream and other dairy products. It's a good idea always to carry some hand sanitizer in case you can't find a place to wash your hands.
Children particularly need to be protected from sun when travelling. In most Asian, Australian, and Caribbean destinations sunrays are much more powerful and thus also more harmful than in Northern European countries. This is, of course, easily forgotten once you finally start your long-awaited sun-filled holiday in the middle of the darkest winter.
Wishing you trouble-free travels!