I still remember the first patient I saw in intensive care. A naked man, covered by a white sheet, was plugged into banks of machines through cables that radiated from his body. His face was covered by a breathing mask, his blood connected to bags of fluids. Muted and voluntarily immobile, so as not to break the fragile web that kept him alive, his eyes tracked me as I entered the cubicle. Intensive care can be a disconcerting place.

As a treatment, it is remarkably successful. Perhaps the greatest tribute to the people who work in critical care is this simple fact: most people leave intensive care alive – despite being dangerously close to death when they arrive. Through a combination of dedication, decision-making and technology, critical care staff ensure that most people pull through. This is the result of years of careful research that has focused clinical practice on restoring the body's functioning as quickly and efficiently as possible.

But recently there has been a dawning realisation that the impact of intensive care extends beyond the survival of the body. Dorothy Wade is based at University College Hospital in London and is one of the country's few intensive care psychologists. She led a recent study which found that more than half of patients assessed at follow-up had marked psychological difficulties. "We learned that patients were suffering from serious depression or having frightening flashbacks and nightmares to their time in intensive care," says Wade. "This badly affected their quality of life and also held back their physical recovery from their illness."

In another study, recently submitted for publication, Wade interviewed patients about the hallucinations and delusions they experienced while in intensive care. One patient reported seeing puffins jumping out of the curtains firing blood from guns, another began to believe that the nurses were being paid to kill patients and zombify them. The descriptions seem faintly amusing at a distance, but both were terrifying at the time and led to distressing intrusive memories long after the patients had realised their experiences were illusory.

Many patients don't mention these experiences while in hospital, either through fear of sounding mad, or through an inability to speak – often because of medical breathing aids, or because of fears generated by the delusions themselves. After all, who would you talk to in a zombie factory?

These experiences can be caused by the effect of serious illness on the brain, but painkilling and sedating drugs play a part and are now used only where there is no alternative. Stress also adds to the mix but is often caused inadvertently by the way intensive care wards are organised. "If you think about the sort of things used for torture," says Hugh Montgomery, a professor of intensive care medicine at UCL, "you will experience most of them in intensive care. As a patient, you are often naked and exposed, you hear alarming noises at random times, your sleep-wake cycle is disrupted by being woken up for medical procedures through the night, you will be given drugs that could disorient you, and you will be regularly exposed to discomfort and feelings of threat."

This has led to a recent push to reorient treatment toward reducing patient stress, and long-term psychological problems, without sacrificing life-saving efficiency. Take this simple example: a study led by consultant critical care nurse John Welch at UCL found that the pitch or tone of alarms on intensive care equipment has no relation to how urgent the situation is. Many frightening-sounding alarms are just reminders – this bag needs refilling in the next hour; don't forget to change the filter – and are often left until more important tasks are finished. But, to the uninitiated, it might sound as if death is imminent and no one is responding.

Some stress is simply an unavoidable part of necessary medical procedures. Breathing tubes inserted through the mouth or surgically implanted through the neck are notoriously uncomfortable. And, despite the survival rates, people die in intensive care. A daunting experience if you're a patient in the same ward.

Helping patients with their intense emotional reactions, whether they arise from hallucination, misunderstanding or medical intervention, normally happens on an ad hoc basis and for many clinicians it is a relatively new situation that hasn't been incorporated into standard training. In many intensive care units, the approach was to sedate patients for the whole of their admission. As this practice declined, for the first time, clinicians were faced with distressed, possibly hallucinating, awake patients.

Wade is currently working with clinicians to take a more systematic approach to detecting and reducing psychological distress. "There have always been experienced or just naturally empathetic nurses and doctors in intensive care," she says. "We're trying to build on that natural care and compassion by teaching nurses and doctors more about the causes and nature of psychological distress… and training them with simple psychological techniques that could help to reduce immediate and long-term distress."

For his part, Montgomery is less convinced about early intervention. He feels intensive care needs to be reorganised to reduce stress but psychological problems are best dealt with in follow-up clinics.

The best time for treatment is the subject of an ongoing debate, but for the first time studies have been funded that will answer these questions. Intensive care is being rethought and may become, at least psychologically, less intense.