I had the exact same thing happen to me, these days even a cup of coffee gets me stimulated and anxious. I've experienced many different problematic events which could have contributed/caused my issues, or it could simply be down to general drug usage. On one occasion which I personally believe started my inability to handle stims about 2 yrs ago (2 weeks of using 3FPM in the day with meager nourishment, stupid I know), I thought I was having a heart attack, I briefly lost feeling in my extremities and had some confusion, unfortunately I had no benzos on hand. I was admitted to hospital briefly by the EMTs due to my extremely high BP/HR despite having calmed down a little, albeit with no follow-up tests. Since this, I've had many ECGs and one echocardiogram which have determined there to be nothing wrong with my heart. This realisation certainly helped me calm down in general, though I'm still convinced there's been lasting harm to my brain (not necessarily from stims). I recovered at some point and started using MPA (I used both 3FPM and MPA as functional stims), after a period of usage similar to the first I developed parkinsons-like symptoms (involuntary shaking, random twitches and shit) which persisted for a few weeks after cessation. I recovered from that as far as I know though this could of well been the last time I enjoyed NDRI/NDRAs normally, not sure. Certainly after this period I can't remember using stims and getting euphoria/motivation/focus from them, only heart-pounding, extreme body-load dysphoric experiences. Hence why: I've completely quit the stims and not touched anything for around 8 months now, I've improved a little bit (I've had many other possibly unrelated symptoms from poly-drug use such as deficiencies in memory recall and formation, problem-solving, language, fatigue and emotional state which has settled at apathetic). I personally feel as if the inner monologue in my brain has diminished as well as my ability to hold train-of-thoughts and spontaneous thought. Though in regards to the stimulant issues I've cut-out even caffeine and don't feel half as anxious as I once did. Still, I've tried a few stims recently and had unenjoyable times, at least I've finally learnt that and will not be using stims for a long while. The anxiety is most likely psychological, I've had an MRI of my brain and am getting the results soon, at least this will confirm any suspicions of it being physical and help me move forward. EDIT (update for posterity): MRI showed nothing of note NB: It was nicely paragraphed but chrome removed the formatting.
