Sudden head rush coupled with brief dizziness. minor headache dry eyes, brain fog afterwards. (normal mri) thoughts?

Sudden low BP: It sounds like your blood pressure is dropping briefly. When this happens, you will get dizzy, possibly get a headache and your brain can feel foggy from a brief lessening of oxygen. With the dry eyes as well, it sounds like you may be dehydrated. You are in a heat wave. Make sure you keep your fluids up. If it worsens, go to the er for IV replenishment.