What can cause sudden dizziness?

BPPV: Benign paroxysmal positional vertigo is a n inner ear problem where the crystals inside the ear are dislodged and then caught in the semi-circular canals causing the dizziness. Other possibilities are: low blood pressure, low blood o2, low blood sugar, or hyperventilation, yo name a few.

Many things: The cause of your dizziness can only be determined by a careful history in regards to what you experience when you feel dizzy, how long it lasts, what other symptoms it is associated with you. The determination begins with your doctor.