I was taking thiamin mononitrate (500 mg) for a few days as well as a sublingual form and I didn't feel any difference. However, that all changed when I started on Benfotiamine. Immediately I felt a drop in my blood sugar, which is an expected side effect, so I know it is working. Ofcourse, I'm sure to eat something every few hours to avoid hypoglycemia. Last night, I had terrible insomnia for the first time in a long time. Today, I've felt fatigued all day and have had a terrible headache. I take this to mean a worsening of my symptoms, so I'm hopeful the benfotiamine is working. Again, I really feel bad, I have a headache and I have to eat something constantly to keep my blood sugar normal. My main complaints from Dysautonomia are dizziness, nausea, orthostatic hypotension, constant thirst, my eyes feel irritated all the time. Not to mention, I have bradychardia, fatigue, depression, terrible, terrible anxiety and the list goes on and on. I also have social anxiety and this is taking a terrible toll on me. I also have a mitral valve prolapse, and a 2nd degree AV block (wenckebach). I did a little research on the AV block and the 2nd degree form is found typically in patients with, you guessed it, a thiamin deficiency! I realized I also had IBS for a while but that seemed to improve since starting on L-Glutamine. That really made a difference for me. I also take a bunch of other supplements, including magnesium. Most of them are for the treatment of symptoms that I hope thiamin supplementation will take care of and replace them. I first learned of thiamin and its role on Dysautonomia from a review on Iherb. When I googled, it lead me straight to this site! I'm very grateful for it. I'll keep you guys posted. As a last resort, I'll try the transdermal cream. But I know myself and I lack the discipline to apply it every day. Taking a pill just seems easier for me. Waterbaby, do you take anything else besides the TTFD and transdermal magnesium? One more thing, I get very, very dizzy and nauseous? Does this happen to anyone else? What's interesting is that I've had this problem since childhood. Maybe I've had Dys. since childhood as well and never knew it.