A headache can be a symptom of many conditions. The symptoms you described ("headache, blurred vision, dizziness, pain in the left side and the top of the head"), indicate that you might be suffering from a so called vascular headache (migraine). A migraine includes episodes of severe and moderate headache lasting from several hours to several days accompanied by heightened sensitivity to lights and usually gastrointestinal problems (nausea, vomiting). Another causes for headaches include myogenic, inflammatory, cervicogenic ones. You may consult a neurologist for an expert opinion.