What can go wrong in Mindfulness Therapy as used in Clinics? I just stumbled across the article Mindfulness therapy comes at a high price for some, say experts. Even when mindfulness is practiced correctly, side effects may occur, like feeling lost or disconnected from the world. What could be the cause of the side effects? Do these techniques deviate a lot from the Suttas or orthodox practice? Do the staff have the necessary training and awareness required to give meditation advice (Kammaṭṭhāna)? Can something be wrong with how the clinic administers the training / teaching?
This is a real phenomenon and it is discussed in the Visuddhimagga and the writings of the Mahasi Sayadaw. Some of the stages of insight knowledge can potentially manifest themselves in this kind of way. I think for most people these stages are relatively easy, but I suppose for some they could be much more difficult. Just from my own practice I can say that these particular knowledges can be very mild

It really is just the result of seeing impermanence on a direct level. When one has a lot of attachments this is not a fun experience because one is holding onto things while at the same time seeing the suffering involved in clinging. The answer to this is that one needs to accept that this is part of the practice and a part of giving up attachment, and continue to practice. Eventually one will let go and move on and progress.

This is actually one of the reasons why I personally have reservations about practicing mindfulness meditation in a purely secular context. The teacher probably won't know about this and without understanding general Buddhist doctrine it isn't possible to understand how to move on.