My salicylate-sensitive teenage daughter started having scary episodes at school where she seemed to zone out for 15 minutes or more, staring at the ground, not responding, as well as other longer lasting episodes, where she was confused and shaky, with red cheeks, and described afterwards that she was aware of some things while it was happening, but it was like she was hallucinating. We think of these as hypo-episodes and have tightened up on her diet. They've been diagnosed as absence seizures but a brain scans recommended by a neurologist didn't show any abnormalities. 

The most recent presentation is for things to happen that she cannot remember doing. e.g. one day I found her in the bathroom scrubbing at her arms, trying to remove intricate patterns of drawing from her left arm. She was upset, and said she could not remember drawing it, she first noticed it at lunchtime. The patterns look like those I've seen her draw quite often. She has previously shown me writing in notebooks that she can't remember writing, some of it not in English! This type of episode had been happening along with "absence seizures" and also full-on "hypo-episodes".  We  have not had reports of absence seizures or the hypo episodes for some time, but how can you be sure that the absence seizures are NOT happening; they are so subtle.  Over the time that these episodes have been happening, her maths performance and attitude has dropped off dramatically, to the point that she now refuses to even try. 

Update one year later: When her dental braces were removed, we finally discovered  that our daughter's "unexplainable" neurological issues over 3.5 years had been due to a reaction to the nickel in the stainless steel.  Many things have settled down now, but it's been quite a journey. - by email