Violet* said she can remember the exact moment that she started to think about killing her boyfriend.
"I was about halfway through watching A Clockwork Orange, and the question popped into my head: What makes someone a serial killer?
"And then another question popped into my head: How do I know I'm not a serial killer? Then immediately after that, almost testing me, an image popped into my head, of me strangling my boyfriend there on the bed."
Violet suffered from extreme episodes of intrusive thoughts. Defined as unwelcome impulses that temporarily block our mental clarity. Intrusive thoughts affect 0.6 percent of the population, and the majority of those are female sufferers.
Although a lot of us will have experienced these episodes in our lives—be it letting a dog off a leash or placing a toe on some train tracks, they are infrequent and can be controlled. For extreme anxiety sufferers, they have the ability to destroy lives.
"Intrusive thoughts can be paralyzing," says Professor Dinesh Bhugra from the World Psychiatric Association. "They are recurrent and persistent."
OCD sufferer Violet found her urges so paralyzing that her world outside of these thoughts was put on hold. Suffering with periods of anxiety and depression in her life, Violet found that once the idea of hurting her boyfriend entered her head, she soon started to think of hurting members of her family, and even her teachers at the time.
"The day came when I decided I had to tell someone what I was going through—not because I thought I needed help, or that I was suffering from a mental health problem, but because I had convinced myself that I was a serial killer, or rather, my anxiety had," she said.
Read More: Living with My Mother's Mental Illness
"Over the following weeks and months, the fear just became worse and worse and worse. The more I tried to not think about the images, the more they just popped into my head. It became physical too: palpitations, light-headedness and nausea."
When the attacks accelerated, Violet saw the visions as taking a life of their own, and at the peak of the episodes, begged her parents to take her to a police station.
"There was no part of me that actually wanted to do the things I could imagine—in fact it was the opposite. But I couldn't convince myself that there was anything that separated me from a murderer."
As well as causing sufferers to fear for the people around them, the visions can take immensely taboo proportions, which is seen in the case of Georgia*, a generalized anxiety disorder sufferer who was disturbed by visions of having sex with her father.
"I had a dream, a really vivid dream, and it makes me feel sick even saying it out loud—I had a dream where I was having sex with my dad. The worst part was, in the dream I felt like I was enjoying it," she said.
"I know it was just a dream, but even knowing that I had the capability to even think up a dream like that majorly fucked with me. It left my head and became a part of my reality. I was only 13, for God's sake. What 13 year old thinks like that?"
Fraught with self-loathing and fearing judgment from those around her, Georgia, like many other sufferers, felt her anxiety grow worse. Her urges became alarmingly frequent, and she soon couldn't trust herself to be around her Dad.
"I avoided my dad like the plague. We were really close before that, but what could I do? Either way, the consequences of my thoughts were terrible for both of us. I felt so dirty. It was only when I moved out a few years ago that I was able really regain some of that closeness with him."
Trying to avoid the triggering thoughts, Georgia found herself developing nervous tics when the thoughts of her dad entered her head.
"I did the stuff you'd expect, the skipping of odd numbers, avoiding cracks in the pavement, paying extra attention to superstitions. I started thinking about having sex with more and more people I didn't want to—family friends, people in the street, and at one point, even animals."
"The more you get on a particular subject and if they are upsetting or distressing and having a negative impact on oneself, the more likely they are to affect a sufferer," says Dr Shamila Moodley of Nightingale Hospital in London. "Intrusive thoughts can influence a person to think of deliberate self-harm or suicide, and then the need to address [the illness] is paramount."
Although Violet soon discovered that her parents had also experienced intrusive thoughts in their lives, Georgia never wants to speak to her family about her experiences.
"There is never an appropriate moment to tell people that you've spent the past ten years avoiding images of having sex with your father," said Georgia. "I can't tell it to my partners, my friends, and no way in hell can I tell it to my family. They refuse to acknowledge my GAD, never mind the symptoms of it. It's only recently that I even realized these ideas as a legitimate thing, and knowing I'm not alone is nothing short of gold dust."
Although Violet now rarely suffers from any urges, she recognizes the conflict that she had to overcome to become in charge of her own mind again.
"Even though I'd felt relief when I realised that these thoughts were a lot more 'normal' than we give them credit for, I didn't trust myself at all. It took another six months of intensive CBT therapy to get back on track and help me get back in control again—by which I mean, to trust myself again."
* Name has been changed