It can be bittersweet, and unsettling (Picture: Getty Images)

One of the most popular books of the moment, Really Good, Actually, by Monica Heisey, describes the pain of bumping into an ex unexpectedly.

It’s an experience we all hope to avoid: you’re going about your day, and suddenly, there’s a very unwelcome blast from the past.

It’s often an uncomfortable and painful experience – and one that might even make you feel like you’ve gone back a few steps in your recovery from heartbreak.

Caroline Plumer, psychotherapist and founder of CPPC London, says: ‘Even if you feel you have moved on, unexpectedly seeing an ex is nearly always an uncomfortable and somewhat emotional experience.

‘Initially, there’s the shock – you were minding your own business and suddenly there they are.

‘There’s the jarring experience of being confronted with someone who you were once very close to, and probably knew a lot about, but who you now have little, if nothing to do with.

‘It can also be a reminder of both the good and bad – there may be sadness over the loss of this person, or anger over how they treated you or how it ended, or quite often a mix of all the emotions. If they are with a new partner, this may further throw you off balance too.’

The first thing to recognise is how normal it is to feel thrown by a small, unexpected sighting.

However, you can get yourself back on track – maybe faster than you think.

How to move forward again

It’s best to keep the moment brief, if you both talk, and to continue on with what you were doing before, taking a moment privately somewhere else if you need it.

Definitely don’t use it as an excuse to make further contact.

Caroline says: ‘Progress is never linear, so if seeing your ex makes you feel upset or uneasy in any way, this is completely normal and definitely doesn’t negate any of the moving forward you have already done.

‘We tend to be very hard on ourselves and see any small wobble as a setback rather than the natural, expected part of life we should view it as.

‘Try your best to accept that seeing an ex is bound to bring up emotions – you don’t need to ignore those emotions, but you can choose to acknowledge them, not judge yourself for them, and move on.’

She recommends using mindfulness to get in the present moment, away from your ex, by focusing on the sights, smells, sounds, and textures around you.

Noticing emotions, but not judging them, is also a popular mindfulness technique, used frequently by the app Headspace.

You can also try breathing techniques, like box breathing, to help yourself get grounded again.

Box breathing works by: inhaling through the nose for a count of four, holding it for four, then releasing for four, and repeating the process.

‘For some people, once they get over the initial shock of seeing an ex, and the adrenalin drops, they may feel fine pretty quickly.

‘For those who have more complex feelings about their ex (even if they weren’t aware they did), it may take longer to get back to an even keel – perhaps they might struggle throughout the rest of the week.

‘If it is taking longer than this to feel better, this is when it is probably worth taking a closer look at your feelings and trying to investigate what is really going on for you, perhaps with a friend, or ideally with a professional counsellor or therapist.’

Emotional recovery isn’t a straightforward process, so you can show some compassion when bumping into an ex causes more hurt.

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‘You were minding your own business and suddenly there they are.’