As mentioned above, profuse sweating and fever can dehydrate the body relatively quickly, particularly with a child or an elderly person. Also, as the amount of water in the body reduces, mucus becomes thicker and even harder to drain. Dehydration can also cause muscle cramps.
Oral re-hydration is the best way to prevent it. These solutions are commercially available, and are special mixtures of salts and minerals which are lost while sweating, vomiting or having diarrhea. Some patients avoid drinking water because of a severe cough, but maintaining water intake should be a priority in such situations.