hi there, you havn't mentioned your age and your general health status. As you have rightly pointed out your feeling of fatigue
and dizzyiness could be due to dehydration
and so please do consume plenty of fluids especially those with electrolytes like coconut water or enery drinks. Your chest pain
may be a manifestation of anxiety
related with the donation of plasma or it could be any organic cause. It would be wise to go to the ER and get an ECG done and your BP checked to be on the safer side. Take care.