Are you sure you are not confusing herx with flare up?
Please elaborate on how you know that Bifidus was the problem.
Are talking about B. Longum?
I have taken handfuls of probiotics, on numerous occassions.
A naturopath I used to see told me B. Longum was the best, so I always make sure it is in the products I guy. It has never caused me any problems.
Perhaps it is competing with something in your system that is dying off and that is why you feel sick.
If not, this is very important information and I will mark your post with an R, and start avoiding B. Longum.