I've been experiences shortness of breath, nausea and headaches about half way into my workout for several months now. I know it's not because I am out of shape and/or I am not used to the workout capacity or load because nothing really has changed in my workouts. I wondering if it's due to some low blood sugar or maybe fatigue from stress and inconsistent sleep lately?
Basically half way through my workout I have a hard time recovering and my lung capacity feels non-existent. I also get the feeling as if I am not getting enough oxygen to the brain and therefore causes me to become nauseous and get a headache. It sucks because I have to severally decrease the intensity and duration of my workouts. Here is my diet:
Breakfast - 3 eggs in tbs coconut oil, 3 slices of bacon, 1 cup beet kvass juice lunch - 10-12 ounces of meat, veges cooked in butter or coconut oil workout (2.5-3 hours after lunch) PWO - coconut water and protein powder Dinner - similar to lunch with some dark chocolate
I am 5'5", 150 lbs and 32 years old. My workouts are a combination of strength/power and conditioning, similar to crossfit football. They are usually not longer than 45 minutes (including warmup) and I workout 3-4 days a week.
One question, how long have you been working out consistently? If it has been longer than 12 weeks, you should take 2 weeks off or at least 1 to see if it improves, to make sure you are not over-training. (Far too many people train far too much.) You won't lose anything, and when you get back into it your gains will accelerate. ( http://suppversity.blogspot.com/2012/01/training-detraining-retraining-build.html Fantastic study/blog here. ) Also the fact that you said this "I wondering if it's due to some low blood sugar or maybe fatigue from stress and inconsistent sleep lately?" makes me say 90% of your problem is probably your over-trained. The other 10% is below.
If you've been working out for less than a year, you should only be in the gym 3 days a week. Especially for Crossfit style intensity, an inexperienced trainee can quickly burn out going the usual 4 or 5 days. (I did it, trust me. I wondered for months why push-ups weren't getting any easier.) If progress has stopped then there are 3 likely reasons as I see it: 79.99% of the time its training too much, 15% of the time you need to change your diet, 10% of the time you need to change your workout, and .01% of the time its not training enough.
Also eat some more carbs, it really sounds like your just hitting the wall, e.g. running out of glycogen. High intensity stuff needs glycogen, end of story. At the very least cycle carbs, eat 100-150g of carbs on workout days, 75g-100g on non-workout days. Eat something like 2 bananas, and a tbsp of honey post workout with your protein shake. Maybe a cup of fruit or a potato with each meal there after. Your working out, you won't store carbs as fat at this level. They will go directly to muscle glycogen. And vegetables don't count. I wouldn't be surprised if this is your entire problem right here. (And I would be incredibly surprised if its neither of the above, considering this is a recent occurence it sounds like.)
And finally, I am not one to often recommend supplementation, but Vitamin D levels have been shown to correlate with VO2max, and its a bit of a foolish thing to supplement one fat soluble vitamins without the others, so you may want to look into that. (Fermented cod liver oil/butter oil, and a d3 supplement is all I take. Or if you eat liver and get sun, that is even better :) )