The poet Horace once wrote that anger is “a short madness”. It is impossible for most people to imagine what kind of madness would lead someone to suddenly snap and attack a child with such ferocity that it is left on a life-support machine. Alberto Izaga, the millionaire City executive accused of beating his two-year-old daughter so badly that she was found bleeding from her mouth, nose and ears, has been sectioned under the Mental Health Act after allegedly going berserk without warning.

It is unclear what prompted the attack. Izaga’s wife Ligia is said to deny vigorously reports that he assaulted the child after she interrupted them while they were having sex at their apartment overlooking the Houses of Parliament. A source who knows Izaga, head of life and health products at Swiss Re, has spoken of the intense pressure under which he works from early in the morning to very late at night “with every decision having to be the right one”.

“You can see people under that much pressure suddenly flipping but Alberto seemed to be so normal,” the source is quoted as saying. Other unconfirmed reports claim that Izaga had said voices in his head told him to attack, suggesting possible mental illness.

Whatever the reasons behind this case, irrational attacks that seem to follow little or no provocation are not uncommon. Only this week a female passenger on a bus in Fulham, West London, knocked a 62-year-old woman to the floor and stamped on her face simply because her newspaper had brushed her arm. The victim needed surgery for her injuries.

The American Psychiatric Association recently defined a condition – intermittent explosive disorder (there is no suggestion that Izaga is suffering from this condition) – when such feelings are recurrent and the consequences serious. It is typified by attacks of impulsive rage that are grossly out of proportion to the supposed provocation and result in property damage, assaults, and injuries and cannot be better explained by a diagnosis of, say, an antisocial or borderline personality disorder.

Sceptics have said that this is simply another name for bad behaviour but many experts say it is a real disorder with a biological basis whereby the frontal part of the brain does not work as well as it should to inhibit the lower parts that are hyperactive in response to threat.

Ronald Kessler, of the Harvard Medical School in Boston, who led a study into IED, says that more than 7 per cent of people in the US have experienced it at some point in their lives. Such people are responsible for serious road rage incidents or irrational acts such as throwing a television set out of a window during an argument. Michael McCloskey, of the University of Chicago, who treats people with IED, has said: “They often say that their anger goes from zero to 100. There is no in between.”

Isabel Clarke, a clinical psychologist who has run anger management groups, says that, generally, when a person feels under threat they undergo physical and mental changes. Their heart rate, blood flow and tension rises as the body prepares for action. Simultaneously the mind goes into tunnel vision as it focuses on the threat and loses the bigger picture. Various factors will then inhibit the average person from acting upon it, such as not wanting to behave violently in public.

However, the fact that there is now increased “social permission” for, say, women to display anger in public means that inhibitors are diluted.

Alcohol, too, is a major disinhibitor. Clarke adds that if an individual is already stressed, say, from a relationship problem or pressure at work then something quite small can make them “flip”.

The Chartered Institute of Personnel and Development (CIPD) issued a report this week which claimed that mental ill health is the second largest cause of sickness absence from work, with stress, depression and anxiety accounting for more than half of these cases.

Ben Willmott, employee relations adviser for the CIPD, says: “HR practioners and line managers need to be able to recognise the warning signs of stress: mood changes, having difficulty with interpersonal relationships, changes in performance, uncharacteristic changes in temper, unusual short-term absences. Working excessively long hours is also a symptom of not coping at work, as well as not taking holiday time.”

The annual absence survey found that over the past three years there has been an increase in stress-related absences. In 1995 the number of people claiming incapacity benefit from suffering from mental ill health was 25 per cent. By 2006, that had risen to almost 40 per cent.

“In other research covering the period 1992-2001, it was found that there was an increase in how hard people perceived they were working,” he adds. “The research found a core reason being technological advances such as the growth of the internet, e-mail, increasing reliance on mobiles and BlackBerries. People indicated that the pace of working life was accelerating and it blurred the line between work and home.

“People, especially those at senior levels, may be able to work from home now because of technological advances. But as a result they may not be able to switch off.”