I experienced those same symptoms (shaky and pounding heart) when I started taking a water pill to lower my blood pressure. My problem was low potassium, which can happen when the body starts excreting a lot of water. Drastically dropping carbs will do that, too, so maybe adding some potassium rich foods could help. I also sip water with 1/4 tsp of "NuSalt" and a squeeze of Mio added. That gives almost 800mg of potassium, and it helps me a lot.