It's the trendy wellness practice that has taken the health industry by storm.

But mindfulness training can trigger unpleasant feelings such as disembodiment, experts have warned.

The popular process involves meditating as part of a bid to feel 'fully present' and aware of each moment, and it is billed as a way of reducing stress or coping with depression and anxiety.

It has grown into a billion-dollar industry and is loved by the likes of Harry Styles, Raheem Sterling and Oprah Winfrey, while 15 per cent of adults in the UK have learnt some form of it.

Now, a study suggests that mindfulness training may cause people to experience altered states of consciousness.

And while some of these experiences can be very positive, that is not always the case, scientists warned.

Researchers from the University of Cambridge conducted a trial to assess the effectiveness of mindfulness training as a way of coping with the stress of examinations.

The team behind the trial followed up with participants a year later to investigate whether they had experienced any altered states of consciousness.

They were asked to complete a questionnaire that explored 11 'dimensions' such as spiritual experience, blissful state, disembodiment and unity.

In experiences of unity there is a sense that borders dissolve and a feeling that we are all part of a larger, interconnected whole.

Disembodiment experiences, however, often consist of a floating sensation or a dissolution of body boundaries – meaning a person can feel disconnected from their own body and mind.

In total, 670 participants took part in the trial. Analysis revealed that people who had received mindfulness training were twice as likely as those in the control group to experience feelings of unity and disembodiment.

Of those who said they experienced altered states of consciousness, 43 per cent experienced unity, 47 experienced blissful states, and 29 per cent said they had disembodiment experiences.

Dr Julieta Galante from the Department of Psychiatry, who led the trial, said it is important for teachers and their students to be aware that unpleasant feelings may arise and to be open to talking about them.

'The most common and intense experiences tend to be those that do not have intrinsically unpleasant characteristics,' she said.

'Some, such as bliss, can feel extremely pleasant. But some experiences, such as disembodiment or altered sense of self could be perceived as unpleasant, or startling, even alarming, especially if you're not expecting them.

'It's important that people who are offered mindfulness are told about the possibility that they may come across these experiences.

'That way, if they do experience them, they shouldn't be disconcerted. There may be nothing wrong with their experience, but it may be useful for them to check in with their mindfulness teacher, and if the experience was negative, to also consider discussing it with their doctor.'

The findings were published in the journal Plos One.