Cipro (Ciprofloxacin) serious side effects. Stop using ciprofloxacin and call your doctor at once if you have a serious side effect such as: severe dizziness, fainting, fast or pounding heartbeats; sudden pain, snapping or popping sound, bruising, swelling, tenderness, stiffness, or loss of movement in any of your joints; diarrhea that is watery or bloody; confusion, hallucinations, depression, unusual thoughts or behavior; seizure (convulsions); severe headache, ringing in your ears, dizziness, nausea, vision problems, pain behind your eyes; pale or yellowed skin, dark colored urine, fever, weakness; urinating less than usual or not at all; easy bruising or bleeding; numbness, tingling, or unusual pain anywhere in your body; the first sign of any skin rash, no matter how mild.