What Causes Dizziness And Headache?

Recently I have been getting dizzy spells and really bad headaches, I went to the nurse on my college campus and she tested my iron, blood sugar, blood pressure and all was normal. The dizzy spells are hard to describe except that it is not like everything around me is spinning, it is like my brain is doing flilpflops and spinning out of control. It has become more intense lately and is mostly when I am laying down or sitting still. What could be wrong?