I've been on Tysabri for almost 9 months now and have not had " the fog" until recently. It is probably just a hit or miss deal and your timing may be coincidental.
I will tell you that after 6 months on the Tysabri, we did an MRI and my doctor found new lesions. Well not new,new, but at less 6 months old new. He was surprised and said that he didn't expect me to have any lesions.(?) I don't know if he meant this soon or what.
Anyway it ends up that I am producing antibodies against Tysabri, which evidently, is not as bad as it first sounds because sometimes you can get over it. (?) (I have to go get rechecked in a few months.)
I hope your tysabri experience gets better, but Im still holding out for a CCSVI cure for you.