Can claustrophobia be overcome?
The NHS estimates there are 10 million people in the UK that suffer from some kind of fear or phobia. Writer and broadcaster Suzy Klein attempts to overcome her claustrophobia - a fear of enclosed spaces.
It is just before 9am on a weekday morning and I am one of around 1,500 passengers crammed into a Bakerloo line train heading into central London.
It is as hot, smelly and crowded as any other morning's commute, but today something is different.
As we stop in a tunnel - a common occurrence for those who regularly use the London Underground - I suddenly begin to feel sick. I have pins and needles in my fingers, my heart is thudding and I can barely catch my breath. Panicked, I fear that I am having a heart attack and begin to shake.
What seems like an eternity later, we pull into Baker Street station and I dash out of the carriage. As soon as I am out, I begin to feel better.
What I have just experienced is not heart failure, but what I later discover to be a panic attack. That was 20 years ago, and I have been dealing with my claustrophobia ever since.
Fear is a natural, and necessary part of our biological hard-wiring. We are programmed to run away from ferocious tigers, to feel frightened of falling from a tall building or being hit by a train.
We do not need to experience these to know that they are life-threatening and fear is our trigger to escape from danger. But what happens when fear begins to take over your life, making everyday tasks impossible?
I set out to find an answer, and quickly discovered that there are surprisingly few kinds of phobias. Most common are the fear of public places (agoraphobia) and fear of confined places (claustrophobia). But less commonly occurring phobias range from a fear of beards and buttons to lightning. All of them seem faintly ridiculous to those who do not suffer from them. Each of them is terrifying for those who do.
I met people with a range of phobias, who had all changed their lives due to fear. I interviewed two sisters with a catalogue of phobias - from needles and tomatoes to travelling on planes.
The comedian Phill Jupitus told me of his deep-seated fear of spiders, lived with since childhood. A grandmother talked frankly about her bitter disappointment at not being able to visit a new baby in the family because of her fear of leaving the house.
Their stories rang with a terrible sense of loss at the pleasures they had missed out on and the misery they had endured.
I also talked to doctors, trying to make sense of phobias from a medical perspective. Dr James Lefanu, who offers public advice on health issues, told me about the medications available such as beta blockers, which dampen the adrenal response and the onslaught of stress hormones during a panic attack.
Online support groups advised on various self-help books, meditation, hypnotherapy. Everyone agreed that the only way to really 'cure' a phobia was by facing it for real - placing oneself in the situation one feared the most.
It galvanised my sense that I had to take my own claustrophobia in hand, so I undertook a course of Cognitive Behavioural Therapy (CBT). CBT promised to 'rewire' my brain, retraining my thoughts not to wander-off into mindless panic and make me look clearly at the world around me.
After several sessions of talking, on 16 March I got on the Tube again for the first time in two decades, joined by Paul, my therapist.
I can only imagine what the commuters on the Tube that morning made of me talking into a microphone about how scared I was - but I did it. I stayed on the train for an hour and a half and was immensely proud to have done it.
Today, I find myself still frightened by the prospect of getting stuck and I continue to worry about whether I will cope. But I have come to understand that phobias are complex beasts, and not easily slayed.
CBT was not a cure but a beginning, and getting on that train was only the first part of a long journey. Now all I have to do is take a deep breath... and get back on the Tube again.
I'm Suzy And I'm A Phobic is broadcast on BBC Radio 4 at 11:00 BST on Friday 17 August.