It started when I was six weeks pregnant," says Lara Basini, 28, a Bristol midwife. "I'd be in a shop and suddenly feel like there were 100 magnets dragging me to the floor. It was like being hit by a stun gun." Her dizzy episodes worsened, until she was bedridden, unable to care for her new baby. It would be a scary and debilitating three years before she was given a correct diagnosis.

Balance disorders are among the 10 most common conditions seen by GPs and over half of us will experience one at some point. While a spot of room spin may sound minor, the reality can be anything but.

There are about 350 recognised balance disorders, which can often be symptoms of other health problems. Diagnosis, therefore, is extremely difficult. "Dizzy patients are 'heart sink' patients," says Andrew McCombe, spokesperson for ENT-UK and consultant Ear Nose and Throat (ENT) surgeon at Frimley Park Hospital, Surrey. "It can take a very long time for doctors simply to decode the language people use to describe their symptoms. Words such as wobbly, woozy or faint don't really tell us what we need to know."

Narrowing down a root cause requires great expertise and the Royal College of Physicians have called for more balance disorder specialists.

The most common type of dizziness is probably vertigo - the false sensation of movement, like when you step off a boat or a big wheel and everything continues to undulate (fear of heights is, properly, "acrophobia"). Vertigo generally signals an inner-ear problem. Acute labyrinthitis is the most prevalent of these - a temporary viral condition that causes sickness and disrupts the balance. It usually clears up on its own, says McCombe, though patients may need medication to help with the sickness.

Vertigo could, also, be a sign of Ménière's disease, a disturbance of the fluid balance in the inner ear that causes hearing loss, tinnitus, sickness and prolonged dizzy episodes. This affects approximately 50 per 100,000 of the population and although it tends to resolve itself, it may go on for months, or even years. Sufferers can become isolated - afraid even to leave the house in case they have an attack. Many end up with permanent hearing loss (usually in one ear).

A fleeting but dramatic "roller coaster" sensation could signify another common inner ear disorder, "benign positional vertigo" (BPV). This is often caused by a head injury, or the degenerating effects of ageing. With BPV, tiny crystals, or "ear rocks", develop in the inner ear and rumble around, disrupting your balance mechanism. Usually, this happens when you turn over in bed, or tilt your head backwards to look up (which is why it is also called "top shelf vertigo"). Although BPV tends to clear up on its own, it can be terrifying, even dangerous if, say, you are at the wheel of a car. "Some people get "drop attacks" where they are poleaxed without warning," says McCombe.

The inner ear, however, is not always the culprit. Light-headedness, giddiness or a spaced-out sensation can be associated with panic attacks, depression or anxiety disorders. And the feeling that you are on the point of blacking out could suggest a circulatory problem (the brain not getting enough oxygen). While a tottery, unsteady sensation ("disequilibrium") might even suggest serious problems such as multiple sclerosis or a brain tumour. In the absence of diagnosis or treatment, it is little wonder people panic and become depressed.

After Basini gave birth to Isaac, now two, the dizzy episodes worsened. She began to vomit and pass out up to 10 times a day. "I'd struggle to stand up long enough to sterilize a bottle," she says. "I couldn't even go to the local shop. It was like being horribly drunk with room-spin and nausea the entire time." She did not leave the house for seven months. Her surgeon husband, Steve Morgan, cut his hours and changed surgical specialities to care for her and their baby.

One problem with a balance disorder is that there are no external symptoms. "People thought I was exaggerating," she says. Even her GP suggested it might be depression. "But I knew it wasn't in my mind." The symptoms became so dire that when doctors wrongly diagnosed a brain tumour, she actually felt relieved. "If it's cancer you either die or survive: I knew I couldn't live like this any more."

After 14 months she saw an ENT specialist who diagnosed an inner-ear problem called vestibular neuronitis. But after three months of balance rehabilitation exercises the spinning sensations got worse. Finally, almost two years later, Basini heard from a medical friend about a little-known speciality called neuro-otology (the treatment of balance disorders). She tracked down Dr SS Surenthiran, a consultant neuro-otologist who runs the Balance Centre at the Medway Maritime hospital, Kent.

Surenthiran swiftly diagnosed "migraine associated vertigo", one of the most common conditions he sees. Since Basini had only ever experienced one migraine, which was during her pregnancy, she was sceptical at first. He put her on a special diet (cutting out triggers such as chocolate, cheese, MSG, dairy and citrus), and prescribed a migraine prophylactic. Almost immediately, she began to get better.

Basini's case is worryingly common says Surenthiran. When the Balance Centre conducted a study of its patients this year they found that on average it took people 44 months to arrive at their door. During these months patients typically saw their GP about eight times and made four or five visits to two other hospital specialists.

"By the time they get here they'll have had months of referrals," says Surenthiran. "They'll be on long-term sick leave, taking early retirement, facing house repossession. There is a vast strain on the family and a sense of worthlessness and despair."

Surenthiran says he is able to give a diagnosis 95% of the time. "You can see the weight lift off their shoulders," he says. "They often say, 'Thank God, I'm not going mad.'" The study showed that on average patients are 70% better nine months after they first visit the clinic.

Basini, for one, says she is "almost normal again". She can now take Isaac to the zoo, the fairground and the park, all impossible before. "I owe that man my life," she says.