ginseng reaction?

Our 17 year old son has had two different episodes of passing out (not just a quick faint, but OUT). Both times he had been taking ginseng before hand -- the first time for several months as part of a well-regulated multi-vitamin, the second time for about a week with some "advertorial" mail-order capsules which were probably much stronger and not necessarily consistent in dosage.

All doctors seem to feel this is a mere coincidence and not worth pursuing -- but I would like to find out if others have perhaps had a similiar "allergic" reaction.