I have low BP naturally and sometimes get faint. and in the last few weeks i have had quite a few of these spells too.... spoke to OB about it and she said this timeof preg can cause it and to lie down or sit down when i feel it come on so i dont faint (legs in air is best) and also to have some sugar/dried fruit/juice/lollies in my bag just t get m blood sugars back up.. so same advice everyone else has posted!!!! It feels pretty awful but unless it happens a LOT i dont think it is anything serious - I would think the main thing to worry about is hurting youself when you faint so get down low as soon as you feel anything! hope it passes soon....