@debored13 - that is a really high dose. I don't think it's a good idea to start anything at a high dose because you don't know how you're going to react and thiamine is very powerful stuff.
I forgot I had started this thread back in 2015. Some time later I started taking 100 mg. of thiamine and had a really nice boost in energy which lasted about a day (2 max) and then I was hit with bad fatigue. I eventually figured out it was due to refeeding syndrome but the problem this time wasn't low potassium, but low phosphorous. This article alerted me to the possibility of hypophosphatemia, the hallmark of refeeding syndrome, the same process which causes potassium to tank during methylation:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440847/
From what I read, supplementing with phosphorous or phosphate is trickier than potassium, you have to go much more carefully. I read that dairy is good source of phosphorous so I drank several glasses of kefir over a period of some hours and that horrible fatigue started to lift. Gradually I was able to increase the thiamine and I'm now taking 300 mg. a day - 150 mg. benfotiamine 2 x a day.
In the meanwhile, my BP seems okay with that and I just drink kefir a few times a week (it's good for my gut too!) I also eat a lot of sunflower seeds which are high in phosphorous (and magnesium).
I am learning that everything is interconnected. Thiamine deficiency itself is another facet of refeeding syndrome.
So you could deplete potassium or phosphorous or other Bs with that high of a dose, and maybe other things too. Hypomagnesemia is another potential outcome of refeeding syndrome, so maybe you're depleting magnesium, which could obviously make you tense.
I think it's unwise to play with such a high dose and that it would be much better to go slower so that you're able to deal with whatever reactions you may have. I don't know what my body would have done if I'd started with 1 or 2 grams of thiamine!