The phenomenon described in the article is very obvious to every practitioner - it can happen that for some time you will feel worse (actually I'm surprised that it's only 8%).
It is related to psychological mechanisms of repression, which is weakened during meditation practices. That is why during serious meditation retreats (like 10 days vipassana) some people freak out and they aren't able to finish the retreat. It's perfectly normal and usually has positive effects in the long run. Although sometimes meditator is not able to work through the energies released - he should seek (any) professional help then.