dehydration or electrolyte imbalance...

Yesterday I went with a friend to Birkam/hot yoga for the first time in probably a year. I used to go a lot more frequently in my pre-triathlon years esp in the winter. Anyway I went yesterday in an effort to work on flexibility, start some heat training and hang out with my friend Cynthia. We went to a studio in Bellevue that focuses on Birkam yoga mostly because the studio we used to go to closed... I prepared for the heat by taking a Thermolyte Sodium-Electrolyte Cap, 3 SportLegs and tried my best to be as hydrated as possible beforehand and had a bottle of ice cold cytomax with me for class.
As soon as the class got started I started sweating a lot - way more than I ever remember sweating years ago. Makes me wonder if it is possible to increase sweat rate over time ect... In general the class was good - I could defiantly tell I am stronger these days but still need major help with flexibility. I really enjoyed the breathing exercises and good chance to work on focusing on the present. My biggest issue is that I'm so used to eating and drinking while training that I had a really hard time with only having 2 chances to drink. I could tell by the end that I was very low on every thing - I felt a little dizzy and shaky. I made it though class but as soon as I was done I drank the rest of my cytomax, a coconut water drink and then went to lunch and drank and ate more trying my best to rehydrate.
I was good for an hour or two and continued to drink and eat. But by the early afternoon I started feeling a slight headache that just continued to get worse and I was burning up. It was the same kind of headache I get after races and long workouts. I drank and ate more but it got worse even after taking 2 tylenol. Finally around 10pm I resorted to taking a midol and within 30 min it mostly faded away.

This is nothing new - I have a tendency to get these headache on Sunday nights especially and almost always after races. I'm hoping I just need to find the right combination of calories, fluid and electrolytes. Maybe I need to take more salts caps and drink more during class/workouts.
The last week or so I have tried drinking nuun though out the day but it winds up giving me a headache. so I'm still looking.. This week I'm going to try cytomax during the day and increasing how much I drink dramatically before, during and after workouts (pretty much all day).
I know it is crazy but I agreed to go again on Tuesday morning so we will see if I can figure something out that works and I would guess would benefit the rest of my nutrition/fluid plan for races and training esp in the heat.