If the acid indigestion sensations, the muscle spasms and the shaking always seems to occur right after you take a dose of "medicine", then it is probably them dying off, or trying to discourage you from taking any more, as it is affecting them. I get similar sensations, only not quite as dramatic as yours. I would call it twitching, rather than spasming, although a few times is has been strong enough to make me "jump pretty high".
They are mean and smart. Do not underestimate them. I would probably back off on the dose a little to see if the spasming and indigestion decreases some. If it does, stay on that dose for a while. When the spasming and indigestion is completely gone, increase the dose until you are twitching again.
It is important to give your body a break occasionally. I hit them hard during full moon and new moon, give my body a break afterwards, when they calm down a bit.