I’m currently experiencing that feeling myself. My best guess would be gastric inflammation or a result of norepinephrine/noradrenaline production. Stimulants trick your body into going supersaiyn.. I mean fight or flight mode via a down stream response of increased and sustained hormone production. One of the downstream factors is the sympathetic nervous system. The sympathetic nervous system’s primary role is to activate fight or flight. When your body initiates fight or flight, the response is similar, albeit at much lower levels in order to maintain homeostasis. Stimulant activation dumps supraphysiological levels of norepinephrine/noradrenaline and is typically sustained for extended periods. Fight or flight being an acute stress response, shuts down and bodily function that is not essential to said state, one of which is digestion. So supraphysiological production of hormones over an extended period is effectively putting your stomach on a forced vacation and drawing blood away from the stomach.
Now I don’t know enough to make any definitive conclusions but it seems logical to assume that shut down and blood diverted, is at the very least irritating the intestines causing gastritis. If you have food sitting while shut down, it’s plausible to assume that’s not going to feel too great, and I’d assume having nothing in your stomach wouldn’t feel good either and either one could cause gas to build up with no way out. That for sure will suck
That’s as far as I can approximate with regard to the MA. Vitamin deficiency alone can cause gastritis so that’s worth investigating since MA use can really burn up those recourses.
Hope this helps, I too want to know the cause (I can’t be bothered rn to look into, I’ll get to later though) so hopefully someone more knowledgeable than me can provide some insight.