[aaimnr]

I had similar experience myself. I wouldn't attribute the risk to the retreat itself, however, but to the vipassana method, which tends to evoke insight experiences as quickly as possible, without first calming the mind using single object samatha practice. If someone were to just use classic anapanasati even for 10 days, I think the results would be somewhat different, as when properly praciced anapanasati calms the body and essentially turns of thinking first, which leads to much calmer and more pleasurable transformation of the mind. Insight experiences with active mind during vipassana practice always feel to me like open brain surgery. With some increasing understanding of not-self, however, it gets less and less scary with time.

[mettamage]

Actually in another Burmese method (not Vipassana as taught by Goenka but the other 'big Burmese line', see Mahasi Sayadaw), going 'crazy' is actually part of the path.