I had a sebacious cyst removed on the back of my neck. Four days before that I started on a week course of Flucloxacillin sodium 500 gram (3 per day). Right after the end of the course I came down with a cold (flu?) very sudden. It's unusual for me to come down so suddenly. Could it be a side-effect of the course. Lowered white blood cell count? Appreciate your time to answer. Graeme Foster. -I'm 67, 1.8 metres, slim (not sure of my weight). Had hyperthyroidism six years ago. Have I.B.S. Some arthritis.