Linda Lester had her first panic attack three years ago. She was enjoying a family holiday in Exeter, following a thin line of tourists down a narrow tunnel to see the city’s underground maze of medieval drains, when suddenly it hit.

“It was absolute, physical terror,” she says. “I had to get out. It was a necessity, almost to the point that I would have beaten people down to get past them. One minute I was fine; the next I was gripped by sheer terror.”

She groped her way clear and gradually her shortness of breath, tight chest and racing heart returned to normal. Physically she was fine, but psychologically she was “hugely unnerved”.

According to the National Phobics Society, panic attacks are “short, recurring episodes of intense psychological feelings of fear” accompanied by physical and mental symptoms such as rapid heartbeat, sweating, dizziness and feeling out of control. Panic attacks come out of the blue, reach a peak of intensity within seconds and last up to half an hour, although some people have attacks that last hours.

While extremely frightening, these attacks are physically harmless. In fact, the symptoms are merely an exaggeration of the body’s normal “fight-or-flight” mechanism, triggered by the hormone adrenalin. They are often associated with stress, although they can also be triggered by drugs such as ecstasy, cannabis and caffeine, or have biological causes such as an overactive thyroid gland.

Professor Adrian Wells, a reader in clinical psychology at Manchester University, says: “Panic attacks are more intense than general anxiety, and the symptoms occur more suddenly.” They’re also more common than many people imagine - some estimates suggest as many as 50 to 80 per cent of people experience at least one panic attack during their lives, although Professor Wells puts the figure at about one in 10.

Less prevalent, but more disabling, is a condition known as panic disorder. Sufferers have recurrent panic attacks and develop a fear of the attacks themselves, or fear of fear. “After the first attack, every time I thought about it I felt panicky again,” says Ms Lester. She soon began to avoid places that brought on the anxiety - such as lifts and multi-storey car parks. “The thought of some situations brought on this creepy terror,” she says. “I’m a confident person, but the panics knocked me back.”

Professor Wells says between 1.5 and 3.5 per cent of people develop panic disorder. For some, it becomes so acute that they alter their lives to avoid panic-inducing situations, and some even develop agoraphobia - fear of open spaces. “People with panic disorder tend to misinterpret the sensations of panic in a catastrophic way,” he says. “They think they’re going to have a heart attack or collapse, or they’re going mad. These negative interpretations keep the panic disorder going.”

Perhaps unsurprisingly, teachers are susceptible. “I have treated quite a few teachers with panic disorder,” says Professor Wells. “It’s a stressful job, and stress can trigger the catastrophic misinterpretations that elevate anxiety, lead to a rush of adrenalin and bring on the panic. Teachers also have to perform in social situations, so if they’re prone to any kind of social anxiety, that can trigger attacks too.”

Attacks most commonly start in adults between 17 and 30, but they can occur much earlier. Although they are difficult to diagnose in children, they do happen in adolescence. The problem for teachers and parents is that the experience of fear is an internal, private one and difficult to spot. “What teachers may see,” says Professor Wells, “is pupils acting more anxiously or avoiding certain situations that might trigger their anxiety.”

Which is what happened to Donna Dean. In her late teens, she developed a terror of sleeping alone at night. Now 33, she lives with her fiance in north London, and has a successful career in television. But the phobia remains a living nightmare.

“My fear, basically, is that I am going to be murdered,” she says. “Usually, I love being in the house by myself, but as soon as it gets dark and the time comes to go to bed, if I’m on my own I start to panic. It’s classic horror movie stuff. I start hearing things. I’m convinced that no matter what I’ve done to secure the house, they’re going to get in. My brain starts working at 100 miles an hour - it feels like madness.”

Her only effective remedy is to stay awake until her fiance returns, or to stay with friends when he’s away on business. According to Professor Wells, it’s just such avoidance behaviour that prevents a panic disorder sufferer from challenging his or her negative thoughts.

Cognitive behaviour therapy (CBT) works by helping patients to understand the panic, and inducing situations that let them see their fears are unfounded. “It depends on people abandoning their usual coping mechanisms,” says Professor Wells, who claims that 80 to 90 per cent of people treated with CBT become panic-free. The National Phobics Society also recommends the therapy, along with antidepressant drugs called selective serotonin reuptake inhibitors.

Other therapies include “tapping”, a kind of non-invasive acupuncture that sufferers can perform with their fingers when in a “panicky” situation. This has helped Linda Lester. But for some people, nothing seems to work. Despite trying everything from hypnotherapy to Prozac, Donna Dean has yet to find a successful treatment. “It’s the thing I wish for most,” she says.

The National Phobics Society has a factsheet about panic attacks and panic disorder. Contact the society on 0870 7700456 or via its website at www.phobics-society.org.uk. Cognitive Therapy of Anxiety Disorders: A practice manual and conceptual guide by Adrian Wells, is published by John Wiley at pound;19.99

SYMPTOMS OF ATTACKS

* Physical symptoms of panic attacks can include: rapid heartbeat, palpitations, increase in breathing, chest pains, sweating, shaking, abdominal pains, nausea, frequent need to go to the toilet, hot or cold flushes, choking, shortness of breath, feelings of dizziness, unsteadiness, or faintness.

* Psychological symptoms include: terror; detachment from the outside world (“de-realisation”); feelings of being unreal and cut off from your body (“de-personalisation”), of imminent madness or death, of losing control.