I'd suggest you go and see your GP. Dizziness can occur as a consequence of a wide range of conditions/illnesses etc.
Could just be stress (doesn't mean that it isn't worth seeing the doctor about!), could be blood pressure, blood sugars, an ear infection, anything.
Always worth getting it checked out and if there is a medical reason your doctor will be able to provide you with an evidential letter which can be taken into consideration alongside your exam entries if you're concerned about it effecting your grades.
Best of luck with your exams and I hope you feel better soon!