After 3 days and nights of stomach flu... I was just given ciprofloxacin class 500mg to be taken 2 at once. Once a day. Took at 4pm yesterday. No problem. Took today at 4pm and within 5 mins, felt major nausea, and then threw it up along with a lot of bright red blood. Obviously, I won t take any more... However, I feel weak and shaky and wonder if I need to go to emerg (only thing open now) or how to proceed.