This was also a huge part of what I experienced. When it happened, I would get immediately, overwhelmingly tired and I would have to lay down or fall down. I can recall having to leave my grocery cart right where it was and go out and lay down in the car with the AC on full blast in December. I turned on the AC because I wasn't sure if it was heat that was causing it or what. I was overjoyed when the opthalmologist finally figured it out, just because it validated what I was feeling.

I truly sympathize with you on this one, and I hope you get answers soon.