One in 10 people experience being stalked, and a third still suffer psychological distress a year later, research reveals.
Clare Bernal was harassed and then murdered by her ex-boyfriend
Despite this, stalking is too often thought of as a rare phenomenon or its seriousness underplayed, say experts.
A British Journal of Psychiatry study finds the psychological consequences are severe even among stalking victims who do not seek help.
The authors say more recognition of the desperation that can result is needed.
The seriousness of stalking was highlighted recently by the murder of a Harvey Nichols shop assistant, Clare Bernal, by her ex-boyfriend while he was on bail after admitting harassing her.
While only a minority of cases end in fatality, either through murder or suicide, studies have found high rates of post-traumatic stress, anxiety and depression among victims who seek help.
To determine whether the same was true among people who chose not to seek help, an Dr Rosemary Purcell and her Australian colleagues from Melbourne University sent out questionnaires to 3,700 men and women living in Victoria.
From the 1,844 completed forms that were returned, 196 had reported experiencing an episode of brief harassment for up to two weeks and 236 said they had experienced a protracted stalking that typically lasted for months.
Compared with 432 respondents of similar age, sex and background but who had never been stalked, mental health problems were much higher among those who were victims of stalking for longer than a fortnight.
Just over a third (34.1%) of these still had psychiatric illness a year after the stalking had ended.
Distress appeared to be particularly high immediately after the event, however, and was most severe when the stalking was prolonged.
About 10% of the respondents who had been stalked said they had considered taking their own life as a result.
"This finding alone is disquieting and underscores the need for greater clinical recognition of the desperation that may accompany such persistent forms of pursuit and victimisation," said the researchers.
They said it was completely understandable that people who are faced with repeated intrusions over which they feel they have little control go on to experience longer lasting distress, such as anxiety and depression, as well as more immediate panic and insomnia.
"It is critical that victims of stalking receive appropriate assistance both to end the intrusions and to relieve potentially enduring symptoms of anxiety and depression," they said.
HOW TO DEAL WITH A STALKER
Notify the police
Do not engage or react to the stalker
Document what is happening and when
Inform family and friends of what is happening
Think about personal safety
Dr Jan-Henk Kamphuis from Amsterdam University, said: "This well-designed and carefully executed study adds to the accumulating evidence that stalking can have major psycho medical consequences for its victims.
"It also shows that even relatively short trials of stalking can have serious mental consequences.
"In terms of coping with ongoing stalking, systematic record keeping of unwanted communications and harassment and early police involvement are indicated, and available evidence suggests that victims who cope in an active problem-solving style do better."
Professor David Canter, from the Centre for Investigative Psychology at Liverpool University, advised: "It is essential that the victim does not respond to, react to or acknowledge the stalker in any way, and this must be maintained at all times.
"The law on stalking does require that the victim demonstrate that he or she was under real threat, sufficient to induce real fear. So the victim should monitor and document his or her activities at all times."
He said 25-45% of stalkers will be violent towards their victims at some point during the stalking episode.
Professor Canter recommended that the person being stalked should put various security measures in place, such as ensuring their home is secure and that they travel in public places.
"Family, colleagues and friends all need to be made aware of the threat to the victim, and potentially to themselves as individuals associated with the victim," he added.