If you are that drained that you are light headed, eat SOMETHING. I tend to do a couple egg whites as there is really nothing there but a little bit of protein and it settles well. Anything else is chancey for me in the morning. Almonds are pretty inert as well and you will get some protein, some fats but not enough to completely destroy your diet.
I either wake up w/ a raging I GOTTA EAT NOW OR DIE stomach pains or I'm just fine. If I try to make myself wait to eat, it just freekin' hurts to much.
I, personally, have never gotten lightheaded from HIIT - but sometimes you just feel like you are dragging (for lack of a better explanation), like you are swimming through mud. Wondering if a handful of almonds, or small protein shake, would give a little more OOMPH to the workout FTITM.
But then again, maybe CB will help with that too .....