Feeling defeated and unwelcome

Hi everyone!
Back in July I took advantage of my kids being away visiting relatives and committed to Bikram 3-4 times per week, giving it 100% of my effort. After needing to leave the room the first class, I did my homework and read up on the importance of salt and electrolytes, purchasing 2 different types (including NUUN), and ensuring that I attended an evening class to allow for ample hydration throughout the day. While I no longer felt the need to leave the room, I could not make it through the standing poses without being completely overcome by dizziness and feeling lightheaded and nauseous. While the instructors were initially kind and encouraging, advising me to lay down and rejoin when I was ready, every time I tried again I had to lay back down to avoid falling down. By the end of the month the instructors were clearly annoyed by me, and I was told that perhaps I was “trying too hard” to get Bikram to work for me. I haven’t been back. It is one thing to feel humiliated when the same people saw me laying on the floor for half of the class….again, but it is another to feel that I am a nuissance to the instructor. During that time frame I found I was exceptionally bloated, which I have read here is a sign of being dehydrated, but I honestly do not know what else to do in that regard. In addition, in August (a week or so after my Bikram month), I learned that my thyroid levels were too high (I have Hashimoto’s thryroiditis and take synthroid) and my synthroid dose was lowered. That actually had me thinking that Bikram had kicked my thryroid into gear, which would be fantastic! The point is that I want to try Bikram again. As difficult as Bikram is for me, I recover from the intensity and exertion far better than any other exercise program which typically leaves me entirely wiped out for days. I was thinking of trying a class and only doing one of each pose, in order to (hopefully) avoid having to lay on the floor. I admit to being intimidated by the instructors, so would like advice on the following:

1. Are there other reasons for dizziness and light headedness besides dehydration? After 15 classes there was no improvement in this and some days were worse than others where I had to lay down the majority of the class despite hydrating throughout the day, before, during and after class, and electrolyte supplementation.
2. How should I approach the instructor when I go back? Is asking that they permit me to do one of every pose reasonable? If they tell me to just lay down and wait for the faint feeling to pass, or to drink more water, there is honestly no reason for me to even try again.

Thank you for taking the time to read this and for offering your expertise!

ReneeNY