Intrusive thoughts are a major feature of mental illnesses such as OCD and PTSD, where they cause compulsive behaviours or manifest as flashbacks, but for most, they are just another bothersome feature of life: 80% of us experience obsessive, intrusive thoughts at some time or other, according to a review of studies from 2012, and they aren’t always a sign of mental illness.
Intrusive thoughts often come in the form of memories and flashes of the past: “A red car that you see on your lunch break might prompt intrusive thoughts about a car crash you witnessed years ago, because the car you saw then was also red,” says Dr Marcus Harrington, a psychologist at the University of East Anglia.
A recent study led by Harrington found intrusive thoughts are more common when we’re sleep-deprived. In the experiment, which involved 85 participants, half of the group were kept up all night while the other half slept for around seven hours. Those who had stayed up found it significantly more difficult to suppress unwanted memories the next day.
“We know from other research that when people are sleep-deprived, they find it hard to prevent themselves from carrying out external actions like pressing a button,” he explains. “The same brain mechanisms are involved in suppressing thoughts that we don’t want to have, so it follows that we’d be worse at these when we’re fatigued, too.”
But there’s more to it than that, Martinelli says. Many people find intrusive thoughts become more common when they’re stressed, down or dealing with a lot of change. “We have more access to memories that coincide with our mood,” says Martinelli. “When we’re feeling good, we feel sure that things will work out. When we feel bad, all we can think about is our failures – when we feel self-conscious, embarrassing memories are much more likely to come to mind.”
You can absolutely have intrusive thoughts without them being a sign of a mental illness. “It’s a very normal and common experience,” Harrington says. However, in people with a mental health problem, “they’re recurrent and harder to control”.
“We’ve known for years that a lack of sleep is a risk factor for every mental illness that we know of, but we didn’t know exactly why,” says Harrington. “Intrusive thoughts seemed like an important factor that bridges the gap between the two, across a range of mental health diagnoses.”
When it comes to mental illness, it can be hard to know whether intrusive thoughts are a cause or an effect: “The nature of intrusive thoughts as troubling or shameful can make people more likely to develop a mental illness, while people who experience depression or anxiety are much more likely to dwell on the past,” Harrington explains.
Intrusive thoughts can also come in the form of worrying or scary impulses: to jump from a tall building or punch someone in the face. “Thoughts like this are normal and all of us have them from time to time,” Martinelli says. “It’s when we fixate on them and judge ourselves by them that they can turn into OCD or anxiety.”
Fortunately, there’s lots to be done to prevent this from happening.
How to stop intrusive thoughts in their tracks
Get more sleep
By some measures, a third of people in Britain are chronically sleep-deprived, getting less than seven hours of sleep per night. Harrington’s recent research suggests five hours of sleep is a minimum to ward off intrusive thoughts, and the more the better.
“Our study showed that total sleep deprivation impaired the important brain mechanisms that keep unwanted thoughts from intruding, but we don’t know where the threshold is when it comes to the amount of sleep deprivation that would cause intrusive thoughts,” Harrington explains.
“Of the patients who slept in our trial, those who spent the most time in deep rapid eye movement (REM) sleep proved best at suppressing unwanted thoughts. REM sleep dominates the second half of the night, after the four-hour mark, so it could well be that getting seven to eight hours of sleep makes us best at keeping intrusive thoughts away.”
Don’t fight them
Nothing makes us more sure to think about something than our efforts not to think about it – like trying not to think about pink elephants. This can make recurring thoughts especially hard to tackle, and it’s why the most disturbing thoughts are often the most persistent.
Don’t attempt to force yourself not to think about something, no matter how scary or unpleasant it may be, Martinelli says. “When you do that, you’re actually giving your brain an instruction, so it has to compare each of your thoughts against the ‘pink elephant’ to check whether it’s thought about them,” she explains. This only makes the offending thought or image more likely to crop up again.
At the end of the day, “we don’t have control over our thoughts – we can only try to find ways to make them less unpleasant”, Martinelli says. The best way to do that is by letting them come until they disappear and are replaced with something else.
Look for patterns
Interesting tips are to be found in the themes that underpin our intrusive thoughts. “Try to be curious about why they’re happening, and whether they have something in common,” says Martinelli, who recommends keeping a diary of your intrusive thoughts and trying to join up any dots.
For instance, someone who is very worried about their health might frequently have intrusive thoughts about their teeth falling out, or an ordinary headache being a sign of cancer. “If you see that they’re trying to tell you something, or that they’re all stemming from the same place, then you can start to challenge the beliefs that are causing them or overcome any difficult memories that keep coming up for you,” Martinelli says.
Take away their power
Sometimes, keeping a thought diary “might help you to realise that you’re procrastinating and putting off the things you really need to do, and your brain is distracting you with other things instead”, Martinelli says.
Intrusive thoughts are so distressing in part because they seem important – unlike the many thousands of other thoughts we have every day. This can be especially true for people with OCD, “who worry that their thoughts make them a bad person”, as their thoughts can make them concerned they might deliberately harm someone, says Martinelli.
“But just because we think something doesn’t make it true. We get to choose which thoughts we believe,” Martinelli says. Sometimes she’ll work with a patient with OCD by getting them to wish she wins the lottery, to help them see – when that doesn’t happen – that their thoughts don’t have much power at all.
It’s the same with intrusive thoughts about things that make us feel scared, worried or embarrassed. “Those thoughts only affect how you feel if you believe that they say something about you, or about what’s likely to happen in the future,” says Martinelli. Seeing your thoughts are only thoughts can make them less likely to pop up again.
Change the story
Try changing the ending of an embarrassing memory or a worrying thought in your head. “Picture whatever’s bothering you in your mind, then just as vividly, imagine something completely different happening instead,” Martinelli advises.
The goal isn’t to convince yourself that something else really happened, but rather to interrupt the brain’s distress signal. This technique helps to “disrupt the mental loop demanding your attention”, allowing your mind to recognise there’s no real threat. “Even something absurd, like picturing a UFO swooping in and abducting the person you keep imagining yourself arguing with, can break the cycle and snap you out of it,” says Martinelli.
That said, you first have to understand why the intrusive thought bothers you and the meaning behind it, and accept it’s there – “otherwise changing the story will just feel fake”, Martinelli warns.
Stay in the present
It’s easier said than done, but try not to wallow in the past. Martinelli is also an expert in mindfulness and regularly deploys it in her practice to help patients overcome intrusive thoughts.
“Especially when our thoughts are depressive, we can’t just snap out of them without a change in our environment,” says Martinelli. “Have a glass of water, go for a quick walk or picture a beautiful sunset – anything that takes your attention away from the thought will break the vicious cycle that keeps them coming back.”