What causes a sudden dizziness?

Dizziness: Depends. There are many possibilities especially problems of the brain, ear, and heart. Sometimes sudden changes in posture can cause this and numerous medications. You should report the details of the dizziness to your medical doctor to be examined and properly treated.

Many Causes: Many things cause sudden dizziness. It could be an inner ear problem, heart condition, low blood sugar, vagal response, nerve condition or simply dehydration. If it is a recurring thing, it is time to see your doctor and have it examined further. One time episodes can be a sign of something worse, so unless you are generally a healthy person, evaluation of your dizziness is important.

Vertigo: Agree with previous answers: from an ear perspective.. The most common causes of dizziness would be a viral infection of the inner ear - viral labrynthitis; and benign positional vertigo (bppv). It could also be a migraine variant. Assuming you have no chest pains/palpitations and are otherwise healthy without high blood pressure. If symptoms other than dizziness - go to er or see your primary md.