What Causes Severe Pain At The Back Of Head Along With Blurred Vision?

My sister has pain in the back of the head...just like a hammering on her head for few minutes..nd suddenly she get blurred vision for a while..could you please tell me the reason for this..and what is the problem..she doesn t have history of trauma or injury, but she didn t change her spectacles past one year..and also she has sinus problems.