Heart symptoms question
Got a cardio-related question for you guys. Sorry if this is long, I would really appreciate some feedback, as this has been a persistent issue for me (Summary is available at the end).
Some background: I'm 26yo male with no allergies or medications, normal BMI, used to run frequently over the summer. At the beginning of September I was at a concert and took some (what I thought were) esctasy pills. Clearly bad idea in retrospect, have rarely done amphetamines and the pills were a little suspect. We soon leave the concert; that evening at my friend's apartment I had some overdose or other toxic type reaction... pre-syncope, dizziness/lightheadedness, increased thirst, increased body temp, loss of appetite, taking deep breaths, etc. I considered the ER, and probably should have gone, but rode it out with friends supervision. Mostly ice packs and water, although I felt absolutely terrible for a few hours, like I would pass out at any moment.
Fast forward 2 weeks of feeling mostly normal, I drink a '5-hour energy' on an empty stomach before work and soon have the EXACT symptoms described in the paragraph above. Feeling extremely dizzy, palpitations, about to pass out, etc. I decide to head back home and lie in bed most of the day. The symptoms would not go away, so that evening I went to the ER and told the doc about both episodes. They did ECG, blood test, chest x-ray, all normal. Went back home and was bedridden for a full 3 days. I was referred to a cardiologist where I did an echo the next week, which was rated 'technically difficult', but also came up normal. Finally after feeling better I had a follow up with my GP who reviewed the results, did a 24-hr holter (since I was feeling better, the GP recommended I try a bit of caffeine to recreate the symptoms, which I tried but was unable to recreate most symptoms that day). After reviewing results, GP said I'm fine and there's nothing wrong with me.
Fast forward to pretty much every day since the end of September, and I have recurring symptoms, although to a lesser degree. I have cut out all caffeine/drug/alcohol use from my diet and have made a concerted effort to eat healthier and continue my days as normal. I have not tried running again since these events. I'll randomly have dizzy spells for an hour, slight chest pain, general malaise, or my heart rate will be elevated for no reason (took a shower this morning and found it was 135. sometimes I'll be relaxing and notice my HR is 90+). These symptoms do not necessarily all appear simultaneously, and generally clear up within an hour or so, but may happen multiple times a day and are affecting my life. When they are not occurring I feel totally normal.
Although I am reassured by the test results and my doctor's conclusion, I'm clearly not 'fine' and I'm wondering if something could be missed by those tests. The closest diagnosis I can find online is cardiomyopathy (which lists amphetamine use as a possible cause), although obviously my GP would know better. Could that be missed by an ECG & Echo? Are there any other tests you would recommend to find the root cause?
Summary - Healthy 26yo male with recent stimulant OD experiencing lingering symptoms for 2 months (dizziness, palpitations, slight chest pain) despite normal ECG, Echo, chest xray, blood work. Currently avoiding all possible triggers such as caffeine and strenuous exercise.