If you're getting dizzy you might want to look at electrolytes for better hydration. Also, worth looking at blood pressure fluctuations and Postural Orthostatic Tachycardia Syndrome(POTS). POTS is diagnosed when your heart rates crosses 30BPM whole going from lying down to standing. I'm curious why your blaming it on iron deficiency. Is your hemoglobin also down? Instead of iron supplement better to consider things like Lactoferrin. Also, if you have low stomach acid that leads to iron not absorbed properly in the GI system. Maybe look at some enzyme and hydrochloric acid supplements to see how you do on the iron front