When and why did you take the first 4? You will be fine. Do not take more than 6 in 24 hours. Next time, try taking one or two and give it 30 minutes.
Ibuprofen is a blood thinner, which can cause you to have severe nosebleeds, or unstoppable bleeding from a wound. It can also cause bleeding inside your stomach. It's best to take only one or two to get good results for a headache.