Matt Haig suddenly began to experience intense anxiety, and it affected every aspect of his life.

On a warm sunny day in Ibiza, Spain, Matt Haig experienced a rush of panic so intense that he couldn't get out of bed. He was 24 years old, and had been living in a beautiful villa with his girlfriend, working at a nightclub over the summer.

He'd been drinking a lot and was sometimes worried about what to do with his life, but up until then he hadn't felt particularly depressed. Then the panic began.

For three days, Haig could neither sleep nor get out of bed. The panic was constant, unrelenting. His heart pounded so hard he felt sure he would die.

The key message here is: Matt Haig suddenly began to experience intense anxiety, and it affected every aspect of his life.

At one stage, the feeling of panic became unbearable, and Haig seriously thought about taking his own life. He even went and stood at the edge of a cliff near the villa, willing himself to jump off. But the thought of the pain his death would cause his loved ones held him back.

His girlfriend, Andrea, was, understandably, very worried. She insisted they visit a doctor, who prescribed some tranquilizers. They didn't help much, but at least they dulled Haig’s senses long enough to allow him to return home to the United Kingdom, where his parents were anxiously waiting.

To an outsider, their lives in the United Kingdom might have seemed very peaceful. Haig lounged around the house, read the paper, did some cooking. But his thoughts were anything but peaceful. He was in the grip of a toxic combination of depression and anxiety. While the depression filled him with dark thoughts, making him feel worthless and futureless, the anxiety flooded him with constant panic.

Even a trip to the corner store became a major ordeal. Haig would set off to buy something simple like a bottle of milk, and start hyperventilating as soon as he left the house. He'd start hallucinating that demons were taunting him, or imagine that something terrible was about to happen.

Inside the shop, his anxiety would become even worse. He'd become so overwhelmed by all the products with their bright labels that he could barely find the milk. When he finally found it, he still had to suffer through a social interaction with the cashier, trying desperately to appear normal.