Long time ago post but do you happen to remember if you had any type of reaction when you switched from thiamine to benfotiamine?
I tried that today and it's made me nauseated and gave me a headache. (I get headaches but usually don't get nauseated very often and that was the only change I made today.) The pill I took was 100mg benfotiamine and 25mg thiamine.
I didn't have any side effects from it. Although I started at a much lower dose than you did. Only about 10-20 mg. Maybe the dose you took was too high to start with.