It’s safe to assume that the thought of stalkers alone sends shivers down many people’s backs; having someone watching your every single move is disturbing, at the very least. However, for many people, it is a nightmare that has unfortunately come true.

According to the Stalking Prevention, Awareness, and Resource Center (SPARC), an estimated 13.5 million people are stalked in a one-year period in the US, with women becoming the targets more frequently than men.

According to SPARC, the majority of victims are stalked by someone they know, most frequently by an intimate partner—whether current or former—or an acquaintance.

“Although many victims know their stalkers, and many are in fact people with whom they have had relationships, other cases involve stranger stalking where the victims don’t know if the stalkers are on the other side of the world, or a cubicle on the other side of their office floor,” Wendy Patrick told Bored Panda in a recent interview.

“Stalking is far more common than reported, in part because most people are unaware of the legal elements necessary to prove stalking,” Dr. Patrick explained. “In California, for example, stalking requires that an offender ‘willfully, maliciously and repeatedly harassed or followed’ the victim, making a credible threat of harm intended to put the victim in fear.”

“Stalkers engage in their behavior to provoke a reaction from their victim. But it can be hard to predict who will make good on their threats, which is why stalking victims should report the conduct to law enforcement,” the expert continued, pointing out that stalking doesn’t require a months-long pattern of conduct; in many jurisdictions “two or more” times would suffice.

Needless to say, being stalked is something that can have long-lasting negative effects on a person. “Stalking can be very traumatic and cause disruption of daily living for victims who live in a constant state of anxiety worrying if and when the stalker will make good on his or her threats,” Wendy Patrick emphasized.

Two-in-three stalkers, according to SPARC, pursue their victims at least once a week; some even do it daily, arguably making the lives of their victims a living hell. And while the scenario is hair-raisingly frightening, there’s more than enough content based on it, from the aforementioned TV series, ‘You’, to one of the classics in the music world, “Every Breath You Take” by The Police, which, in case you didn’t know, was a story from a stalker’s perspective.

Back in 1983, one of the band’s members, Sting, said “I think it’s a nasty little song, really rather evil. It’s about jealousy and surveillance and ownership,” summing up the song, which could be considered somewhat romantic, if you didn’t bear in mind the backstory.