Almost everyone has had a feeling of unsteadiness or a whirling sensation in their heads at some point in their lives. Usually it's put down to dizziness, but dizziness is a broad term that can mean different things to different people. It's a common complaint, but it can be serious. It has no specific medical meaning, but there are four common conditions that can be considered types of dizziness:

Vertigo
The feeling of motion when there is no motion such as you spinning or your environment spinning. Spinning yourself round and round, then suddenly stopping can produce temporary vertigo. However, when it happens in the normal course of living, it signals a problem with the vestibular system of the inner ear - the body's balance system that tells you which way is down and senses the position of your head. About half of all dizziness complaints are vertigo.

Light-headedness
Also called near syncope, light-headedness is the feeling that you are about to faint. It is commonly felt by standing up too quickly or by breathing deeply enough times to produce the sensation.
-- Disequilibrium. A problem with walking. People with disequilibrium feel unsteady on their feet or feel like they are going to fall.
-- Anxiety. People who are scared, worried, depressed or afraid of open spaces may use "dizzy" to mean frightened, depressed or anxious.

Frequent dizziness sufferers may complain of more than one type of dizziness. For instance, having vertigo may also make them anxious. Dizziness can be a one-off event, or it can be a chronic, long-lasting problem. Nearly everyone who is dizzy will get better. This is because a person's sense of balance is a complex interaction between the brain, each ear's separate vestibular system, and the sense of vision. When one component breaks down, the others usually learn to compensate.

What causes dizziness?
--- Infection such as the ones that cause the common cold can cause temporary vertigo via an ear infection. This inner ear infection is generally viral, harmless and goes away usually in one to six weeks, but medicines are available if it is severe.

-- Benign paroxysmal positional vertigo (positional vertigo or BPPV) is caused by movement of the otolith - a tiny calcium particle the size of a grain of sand - from the part of the ear that senses gravity to the part that senses head position. The person feels as if their head is turning when it isn't. A two-minute therapy can move the otolith back where it belongs and fix the problem. This therapy, called the Epley manoeuvre, cures vertigo 80% of the time.

-- Meniere's disease is a disorder characterised by long-lasting episodes of severe vertigo. Other symptoms of Meniere's disease are tinnitus (ringing in the ear), hearing loss and pressure or fullness in the ear.

-- Bilateral vestibular loss is a feeling of everything bouncing up and down. It can happen to people who take an antibiotic that is toxic to the ear. It usually improves over time.