Across dozens of novels and well over a hundred short stories, Philip K Dick worried away at one theme above all others: the world is not as it seems. He worked through every imaginable scenario: consensus reality was variously a set of implanted memories, a drug-induced hallucination, a time slip, a covert military simulation, an illusion projected by mega-corporations or extraterrestrials, or a test set by God. His typical protagonist was conspired against, drugged, hypnotised, paranoid, schizophrenic – or, possibly, the only person in possession of the truth.

The preoccupation all too clearly reflected the author’s life. Dick was a chronic doubter, tormented, like René Descartes, by the suspicion that the world was the creation of an evil demon ‘who has directed his entire effort to misleading me’. But cogito ergo sum was not enough to rescue someone who in 1972, during one of his frequent bouts of persecution mania, called the police to confess to being an android. Dick took scepticism to a level that he made his own. It became his brand, and since his death it has been franchised across popular culture. He isn’t credited on Hollywood blockbusters such as The Matrix (in which reality is a simulation created by machines from the future) or The Truman Show (about a reality TV programme in which all but the protagonist are complicit), but their mind-bending plot twists are his in all but name.

As Kyle Arnold acknowledges early in his lucid and accessible study, it would be impossible to investigate the roots of Dick’s cosmic doubt more doggedly than he did himself. He was ‘his own best psychobiographer’: in endless conversations and interviews, not to mention thousands of pages of private journals, he rehearsed the events that had moulded him. They began at birth. He and Jane, his dark-haired twin, were born prematurely and sickly in 1928; their mother was unable to feed them properly and Jane died at six weeks. Dick’s mother, herself chronically ill with Bright’s disease, was haunted and emotionally distant; she and his father soon divorced. At the age of five Dick was anorexic, choked with guilt that his greed for his mother’s milk had starved his sister. He was already taking amphetamines, prescribed for his asthma. Dispatched to boarding school, he withdrew from its cold authoritarian regime into fantasy worlds peopled by doubles and forgotten ‘real’ versions of himself. He was sent to psychiatrists for treatment for his anorexia and anxiety attacks, from which he learned that self-neglect was a route to attention. He remained in and out of therapy all his life and at various points diagnosed himself as schizophrenic and committed himself to mental hospitals.

Psychotherapy sharpened a talent for self-analysis but also for self-deception. In Arnold’s pleasing simile, Dick generated ideas about himself ‘like a cuttlefish emitting ink’ – to conceal rather than reveal. His confessions were unsparing in many respects but they tended to elide his tantrums, his self-pitying histrionics and his betrayals of loved ones: he informed on his friends to the police and during one paranoid episode contrived to have Anne, his third wife, locked up as a dangerous psychotic. Such behaviour was exacerbated by the amphetamines he frequently took in massive doses. Speed made him very productive – from the mid-1950s to the late 1960s he wrote several novels a year – but it also blurred the line between fictional mind games and real life.

Arnold examines these darker tendencies through one of the canonical episodes in Dick’s life story. In 1971 his house in San Rafael was mysteriously ransacked. Dick elaborated endless theories about the perpetrators – from the IRS to the CIA, undercover narcotics police officers to a neo-Nazi gang – but Arnold suggests that he probably did it himself, squaring the circle of his paranoid imaginings by creating a situation in which he was a victim persecuted by shadowy and unjust authorities. At the height of his amphetamine craziness he might have genuinely forgotten the act. Or perhaps it was committed by a malign doppelgänger?

The centrepiece of Dick’s psychobiography, to which Arnold devotes most of the second half of his book, is the epiphany he came to refer to as ‘2-3-74’. This was the date on which he was visited by a dark-haired girl – an archetype he always related back to his lost sister – delivering medication from the pharmacy. She wore a Christian fish symbol around her neck; as the sun glinted off it Dick felt himself pierced by a ‘pink light’. For several weeks afterwards he lay in bed in a semi-trance receiving visions. He time-travelled to ancient Rome and lived a parallel life as ‘Thomas’, a persecuted early Christian. At other times he was penetrated by an all-knowing intelligence that revealed to him for the first time the world not as it seemed, but as it really was.

Dick believed 2-3-74 had changed his life forever, but Arnold stresses its continuity with the dramas that regularly punctuated it. He had similar experiences at other moments of heightened stress and ‘spiritual emergency’ (in this particular case he was struggling to cope with a debt crisis and a new baby, with all the anxieties and abandonment issues that this entailed, and was probably taking lithium for depression). Even while he was still receiving the visions, Dick began rationalising them with sci-fi plotlines. Were they transmissions from God, or telepathic aliens, or a vastly intelligent computer that runs the universe? Or had he, as in The Manchurian Candidate, been programmed with a secret message to be hypnotically triggered at a later date?

In the immediate aftermath of 2-3-74, Dick felt reborn. It had been not a breakdown but a breakthrough: for the first time he had stepped behind the scenery and witnessed the truth. Deep peace flooded him as certainty finally conquered doubt and paranoia was replaced with a sense of divine protection. He had been united with his missing double, his fractured self made whole. Descartes’s demon was vanquished by an empathy with the world that cleansed the human condition of its solipsism and alienation. It was a theme he had often explored in his fiction, notably in Do Androids Dream of Electric Sheep? (1968), in which an ‘empathy box’ allows devotees of a religion to fuse emotionally with their saintly leader.

Dick claimed that 2-3-74 was an apotheosis that saved the world, but it wasn’t enough to save him from himself. As it receded, his life turned out no better than before: he suffered severe depressions, attempted suicide and swapped amphetamines for sedating anti-anxiety drugs. He wrote up his experiences compulsively in a text he called his ‘Exegesis’, in which he interrogated the visions and drew out their resonances with Buddhism, early Christianity, Neo-Platonism and Gnosticism. It grew to over a million words and was never finished (an edited version was published in 2011 as The Exegesis of Philip K Dick). It was increasingly haunted with nostalgia for the fading vision and by the re-emergence of his recursive doubts: had it all been just another trick of the mind, another twist in the maze, another novel masquerading as reality? In the end Dick’s eternal second-guessing and his inability to separate reality from fiction could not be suppressed. At times they may have tipped him into madness, but they were also the wellspring of his art.