Question's for God.

[Little Rik]

It is all relative yog.
By playing chess or do things that require a big mental effort you strain your mind.
If you instead use that mental strength to practice yoga meditation then a positive reward take place.

This is nothing but a bare assertion.

I looked further into the literature. In 1992, David Shapiro, a professor at UCLA Irvine, published an article about the effects of meditation retreats. After examining 27 people with different levels of meditation experience, he found 63 per cent of them had suffered at least one negative effect and seven per cent profoundly adverse effects.

The negative effects included anxiety, panic, depression, pain, confusion and disorientation. But perhaps only the least experienced felt them – and might several days of meditation not overwhelm those who were relatively new to the practice? The answer was no. When Shapiro divided the larger group into those with lesser and greater experience, there were no differences: all had an equal number of adverse experiences. And an earlier study had arrived at a similar, but even more surprising conclusion: those with more experience also had considerably more adverse effects than the beginners.

http://www.independent.co.uk/life-style/...68291.html

Wrong again yog.  

Yoga meditation require not hard work but very very hard mental work.
Out of 100 people who start this practice maybe only one or two continue for sometime
and out of this one or two 90% of them stop practicing after sometime due to the frustration
of not getting an easy and mystical meditation.
Been there done that yog.

When your link say............After examining 27 people with different levels of meditation experience, he found 63 per cent of them had suffered at least one negative effect and seven per cent profoundly adverse effects.....it is obvious that D.Shapiro examined mainly those who fail and therefore I agree with him that meditation may have negative effect but negative effect for those who fail only.
For those who overcome the difficulties is a different story.

The same story apply to anyone who wish to get a degree in something.
Only few people succeed while most of them fail.
I once want to get a black belt in Aikido.
After the few month of hard work I gave up.
I was frustrated no question about it.
That is quite natural that by not succeeding a person feel negative effect.

If this Shapiro wish really to know about negative or positive effect on meditation he should come
to one of mine group meditation and interview those who succeed.

One more important point.

There are different types of yoga meditation.
Not all of them lead to a mystical meditation.
There are certain rules to follow if you want that the meditation lead to a mystical experience and progress.
The most important point is to have the proper mantra.
Only a real guru can do that.
Most of the gurus give old mantras that can not possibly lead in the correct direction.
Other rules are that you close your eyes and keep your spine straight during meditation,
that you follow a vegetarian or vegan diet and several other things.
I don't really know where this guy went to do his research but it is obvious to me that he didn't understand how the system works.