I'm 36 weeks pregnant and have hot flashes and extreme diziness. What can it be due to?

Hormones. Pregnancy hormones (estrogen in particular) can have the effects you mention - although they sound too severe to be garden variety symptoms of normal pregnancy. Please see your obstetrician to assure your blood pressure is normal and your neurological examination unremarkable - alternative explanations include preeclampsia, stroke and migraines, none of which are good. Best of luck!