Dizziness is a word that is often used to describe 2 different sensations: lightheadedness and vertigo. It is important to know exactly what you mean when you say, "I feel dizzy," because it can help you and your health professional narrow down the list of possible problems.

Lightheadedness is a feeling that you are about to pass out (faint). Although you may feel unsteady, there is no sensation of movement.

Lightheadedness usually goes away or improves when you lie down. If lightheadedness gets worse, it can lead to a fainting spell with nausea or vomiting.

Lightheadedness usually does not indicate a serious problem. It is common to feel lightheaded occasionally. Lightheadedness is often caused by a momentary drop in blood pressure and reduced blood flow to the head when you get up too quickly from a seated or lying position. This is called orthostatic hypotension . It may be caused by dehydration or medications such as water pills (diuretics).

Lightheadedness is common when you have flu, a cold, or allergies. Vomiting, diarrhea, and fever can cause dehydration and lightheadedness. Other common causes of lightheadedness include side effects of medication, hyperventilation, stress, anxiety, drinking alcohol, or using illegal drugs. A more serious cause of lightheadedness is bleeding. If a person is bleeding internally, lightheadedness and fatigue may be the first noticeable symptoms of blood loss.

An uncommon cause of lightheadedness is an abnormality in your heart rhythm. This can cause recurrent spells of lightheadedness and can lead to a fainting spell (cardiac syncope). Unexplained fainting spells need to be evaluated by a health professional. See Fainting on See Unconsciousness.

Vertigo is a sensation that your body or the world around you is spinning or moving. Vertigo is usually related to inner ear problems. It may occur with nausea and vomiting. It may be impossible to walk when you have severe vertigo.

The most common form of vertigo is triggered by changes in the position of your head, such as when you move your head from side to side or bend your head back to look up. This is called benign positional vertigo .Vertigo also may be caused by labyrinthitis, an inflammation in the part of the inner ear that controls balance. Labyrinthitis is usually caused by a viral infection and sometimes follows a cold or the flu.

Other underlying problems that can contribute to vertigo are Meniere's disease (a balance problem believed to be caused by a build-up of fluid in the inner ear), multiple sclerosis, and, in rare cases, a brain tumor.