Dizziness is a word that is often used to describe two different feelings. 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 faint or "pass out." Although you may feel dizzy, you do not feel as though you or your surroundings are moving. Lightheadedness often goes away or improves when you lie down. If lightheadedness gets worse, it can lead to a feeling of almost fainting or a fainting spell (syncope). You may sometimes feel nauseated or vomit when you are lightheaded.
• Vertigo is a feeling that you or your surroundings are moving when there is no actual movement. You may feel as though you are spinning, whirling, falling, or tilting. When you have severe vertigo, you may feel very nauseated or vomit. You may have trouble walking or standing, and you may lose your balance and fall.

Lightheadedness

It is common to feel lightheaded from time to time. Lightheadedness usually is not caused by a serious problem. It often is caused by a momentary drop in blood pressure and blood flow to your head that occurs when you get up too quickly from a seated or lying position (orthostatic hypotension).

Lightheadedness has many causes, including:

• Allergies.
• Illnesses such as the flu or colds. Home treatment of your flu and cold symptoms usually will relieve lightheadedness.
• Vomiting, diarrhea, fevers, and other illnesses that cause dehydration.
• Very deep or rapid breathing (hyperventilation).
• Anxiety and stress.
• The use of tobacco, alcohol, or illegal drugs.

A more serious cause of lightheadedness is bleeding. Most of the time, the location of the bleeding and the need to seek medical care are obvious. However, sometimes bleeding is not obvious (occult bleeding). You may have small amounts of bleeding in your digestive tract over days or weeks without noticing the bleeding. When this happens, lightheadedness and fatigue may be the first noticeable symptoms that you are losing blood. Heavy menstrual bleeding also can cause this type of lightheadedness.

An uncommon cause of lightheadedness is an abnormal heart rhythm (arrhythmia), which can cause fainting spells (syncope). Unexplained fainting spells need to be evaluated by a health professional. To check your heart rate, see taking a pulse.

Many prescription and nonprescription medicines can cause lightheadedness or vertigo. The degree of lightheadedness or vertigo that a medicine causes will vary.

Vertigo

Vertigo occurs when there is conflict between the signals sent to the brain by various balance- and position-sensing systems of the body. Your brain uses input from four sensory systems to maintain your sense of balance and orientation to your surroundings.

• Vision gives you information about your position and motion in relationship to the rest of the world. This is an important part of the balance mechanism and often overrides information from the other balance-sensing systems.
• Sensory nerves in your joints allow your brain to keep track of the position of your legs, arms, and torso. Your body is then automatically able to make tiny changes in posture that help you maintain your balance (proprioception).
• Skin pressure sensation gives you information about your body's position and motion in relationship to gravity.
• A portion of the inner ear, called the labyrinth, which includes the semicircular canals, contains specialized cells that detect motion and changes in position. Injury to or diseases of the inner ear can send false signals to the brain indicating that the balance mechanism of the inner ear (labyrinth) detects motion. If these false signals conflict with signals from the other balance and positioning centers of the body, vertigo may occur.