Feeling extremely weak/tachycardia post-fast.

I made it 5.5 days on a water fast. I liberally used electrolytes and drank about 2L of water per day. Near the end, I started struggling with shortness of breath, tachycardia, and low blood pressure. Supplementing electrolytes could not alleviate the situation, so I stopped the fast with an egg and a small piece of cheese. My first question is: did going on a walk that was about a mile each way, with an hour in-between, possibly cause over-exertion? This was on day 5. What are the rules for exertion in a fasted state? Could over-exertion lead to the above symptoms? In the days since, I have slowly refed. I am digesting and moving food through my system. No issues there. However, I'm feeling incredibly weak. I take long naps and cannot wake up easily in the a.m.. I still have frequent tachycardia, though the lightheadedness is gone. Magnesium helped resolve it last night. I've been drinking raw milk for the vitamins and electrolytes. I'm eating normal sized meals 3x/day and drinking lemon water with a few drops of of trace minerals. Is there anything I may be doing wrong to cause this continued weakness? Other factors that may be important: I did not sleep well during my fast. I consume zero caffeine and avoid it whether fasting or not. I have celiac disease, anemia, and other random issues. I did the fast for health reasons. I have fasted in the past, but for 3 days. I was attempting 7. Tips? Advice? Can you relate to this situation? Thank you so much.