This is a concerning symptom. I would strongly recommend that you see your primary care doctor
to have this evaluated. There are many possible causes of this symptom, some are minor and some are serious.
Dizziness can be caused by a few different causes. One cause that is very concerning is known as presyncopal symptoms -- a low blood pressure. This is essentially when the blood pressure supplied by your heart to your body is relatively low and therefore almost causes your body to nearly faint. This can be caused by dehydration, infection, blood loss, diabetes, heart problems and many other causes. Your blood pressure should be checked. This can also be mimicked by loss of blood (anemia).
Another common cause is known as benign positional vertigo
(BPV) which is caused by a problem in the inner ear. This is a more minor cause as it often heals itself, but sometimes needs treatment. Various other inner ear problems can also cause dizziness.
Your associated (potentially) headache
is also concerning. Dizziness is very very rarely associated with a brain mass, but this could be the case.
Talk to your doctor. You should have a full neurologic examination and a blood pressure check. Good luck! If your symptoms are worsening you should urgently go to the emergency room.