Rumorville:  Word is that Krisitina's situation has some similarities to Jason's.

Her symptoms are not a recurrence of her aplastic anemia that she had as an infant.  Rather, they are an indication of some kind of residual disorder that is related to the earlier car bombing.  (This refers to when Sonny planted a bomb in Johnny's car when he believed the two were dating, not realizing that Kristina would be with Johnny.) 
Supposedly, this involves some swelling in the brain.

Needless to say, this will likely have even more repercussions for Sonny.