Today, I sit home with the start of a head cold. I felt it coming on last night. This morning I considered the hints that warned me of the coming inconvenience. In the back of my sinuses, a familiar burning I've come to recognize over the years warned me that by morning light I'd feel less than ideal. Before bed, I experienced aches in my legs brought on by a low grade fever. I tossed and turned, fought chills and sweats and sure enough crawled out of bed feeling rather poorly.
Give a character a cold, flu or some other ailment, but don't tell how they feel, show it coming on. Give details making it real to the reader.