It's your parasympathetic nervous system.. Adrenaline and what not. As normal, the remedy is more drugs. A valium and/or muscle relaxants would probally help. Tums will do absolutely nothing.
Acid always gives me an upset stomach too. And apart from the g.i. symptoms, I've read that it causes uterine contractions for some females, which can add to the shitty feeling.
A light meal before you drop and also take a couple tokes of weed.
It will enhance the trip and settle your stomach as well.
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