My DD has cyclic vomiting. She gets pale, sometimes confused, and eventually vomits--once or several times over an hour or two. She can be very drowsy during these episodes. It can resolve quickly, or she can feel bad for several hours after.
Cyclic vomiting typically follows a recurring pattern, happening every X number of days. DD's came more in streaks, such as every day for a week at the exact same time of day, then not again for awhile. Fortunately she only has these episodes a few times a year now, usually when she is overly fatigued, and sometimes she only feels sick but doesnt actually vomit.
I don't think there's general agreement about the cause of cyclic vomiting, though some think it is a form of migraine (DDs dont include headaches, btw). DD's are believed to be part of her mitochondrial disease, though one doesn't have to have mito to have cyclic vomiting.
I should probably mention, to be thorough, that DD has episodes akin to low blood sugar as part of her mito (her readings actually look ok, but because her body can't metabolize efficiently, she is low on available fuel at a "normal" reading); we dont know if going too long without eating contributes to her CV episodes, but I will say she has had very few since starting on small frequent meals and raw constarch, in addition to her mito supplements (carnitine and CoQ10).
All of this may not relate at all to your DDs situation, but if it rings a bell, do a search on Cyclic Vomiting Syndrome or try looking at cvsaonline.org.
Good luck in finding an answer. We spent years puzzling over of our DD's quirky symptoms, including the CVS, before we found the right doctor who finally put the pieces together and diagnosed her with mito and CVS.