From http://www.sk.com.br/sk-krash.html

Finally, the fifth hypothesis, the Affective Filter hypothesis, embodies Krashen’s view that a number of ‘affective variables’ play a facilitative, but non-causal, role in second language acquisition. These variables include: motivation, self-confidence and anxiety. Krashen claims that learners with high motivation, self-confidence, a good self-image, and a low level of anxiety are better equipped for success in second language acquisition. Low motivation, low self-esteem, and debilitating anxiety can combine to ‘raise’ the affective filter and form a ‘mental block’ that prevents comprehensible input from being used for acquisition. In other words, when the filter is ‘up’ it impedes language acquisition. On the other hand, positive affect is necessary, but not sufficient on its own, for acquisition to take place.

A more critical look is here http://www.timothyjpmason.com/WebPages/LangTeach/Licence/FLTeach/Thunk5.htm

I agree with you regarding the order of events. If that’s all it took, we would have a lot of dyslexics “curing” themselves in the privacy of their bedrooms or living room windowseats.