Can meditation have negative side effects?

In my experience meditation can be harmful which is the reason I stopped teaching open classes and for the last ten years I only teach my clients who I know well and where I can match type of meditation practice with a particular need and personality type of a client as well as have a space in psychotherapy session to process what comes out during the meditation.
When we are talking about meditation side-effects there are three important points to consider:
First, there are different types of meditation and not every type would be suitable for everyone. For example, Budhhist Vipassana meditation is very difficult practice for extrovert types, A type personality or hyperactive people. But “Yoga Nidra” meditation which follows quick pace moving the focus through different body parts would work very well in such cases. Many clients tell me of their failed experience with meditation. Most of the time it is due to applying one specific meditation technique in a group set-up and as a result some people would enjoy it and do well while others may experience frustration and feeling of failure.
Second, in meditation you connect to your internal space and depending on what you stored in your internal space meditation may release emotional and mental blockages, from abuse and traumatic images to unprocessed anxiety, grief or anger. Several researchers described this side-effect of meditation:
1. Kutz et al. (1985a,b) described meditation side-effects such as sobbing and release of hidden memories and themes from the past: incest, rejection, and abandonment.
2. Other adverse effects described (Craven, 1989) are uncomfortable kinaesthetic sensations, mild dissociation, feelings of guilt and, via anxiety-provoking phenomena, psychosis-like symptoms, grandiosity, elation, destructive behaviour and suicidal feelings.
3. Shapiro (1992) found that 62.9% of the subjects reported adverse effects during and after meditation and 7.4% experienced profoundly adverse effects. The length of practice (from 16 to 105 months) did not make any difference to the quality and frequency of adverse effects. These adverse effects were relaxation-induced anxiety and panic; paradoxical increases in tension; less motivation in life; boredom; pain; impaired reality testing; confusion and disorientation; feeling ‘spaced out’; depression; increased negativity; being more judgmental; and, ironically, feeling addicted to meditation.
During retreats that I have been guiding for years, meditation and silence most times cause a release of stored emotional, mental, physical or spiritual staff. The fact is that we have too busy lives and make very little time for processing of emotional and mental content resulting in a huge number of unprocessed “files”. The moment we slow down, became quiet and connect to our inner space material from these “unprocessed files” may come out. In my experience, if one gets no help with processing of that material it can do more harm than good.
Third, meditation practice is often misunderstood and romanticized. Some people think of meditation practice as a way to get relaxed and some as a way to focus. Even though relaxation or focus may be some of the benefits, “goal” in meditation is nothing to do with these. Meditation or dhyana is a process of raising spiritual energy and reaching spiritual enlightenment. In yoga, meditation or dhyana, the process of spiritual awakening is not considered an easy or pleasant one. Hence, on our spiritual journey we need a “guru”. Word “guru” translates as “dispeller of darkness” – reflecting how risky and dangerous that road may be.
In conclusion, meditation is a very powerful practice that can induce unpleasant or even harmful effects if not practiced under the guidance and if “material” released is not processed in a meaningful way.