Hello. Thank you for posting your query at DoctorSpring.com
I understand your concern.
Light-headedness in the middle of the work out can be indicative of a lot of factors, but the commonest as you rightly pointed out is hypotension, or fall in BP, due to excessive loss of salts through your sweat. It can be because of exhaustion of such a strenuous work out. A lot of people drink a lot of water while working out, but it is not just the water you lose, it is also a lot of salt that goes out of the body, hence making the person feel weak and light headed. You need to cut down on your work-out schedule for a few days, or reduce the duration and make sure you're adequately hydrated before you start the workout.
Kindly be very careful, because there have been cases of people passing out during their work outs due to hypotension. Protein has no direct relation, however protein does make a person pee a lot, hence increasing the chances of them getting dehydrated quicker. Hence it is advised to drink more water than normal, in people consuming such protein supplements, also to prevent formation of renal stones in the future.
Hope this was helpful,