Honestly, it sounds like you're suffering from anxiety and panic disorder set off or escalated by stimulant use. This might be accompanied by a cardiac problem in your case (although most people in this situation think it is, and most of them luckily end up being wrong), but everything you've described can be caused purely by anxiety disorders, as ridiculous as that sounds initially.
Sufferers of panic attacks often report a fear of dying or heart attack, flashing vision, faintness or nausea, numbness throughout the body, heavy breathing and hyperventilation, or loss of bodily control. Some people also suffer from tunnel vision, mostly due to blood flow leaving the head to more critical parts of the body in defense. These feelings may provoke a strong urge to escape or flee the place where the attack began (a consequence of the "fight-or-flight response", in which the hormone causing this response is released in significant amounts). This response floods the body with hormones, particularly epinephrine (adrenaline), which aid it in defending against harm.[9]
A panic attack is a response of the sympathetic nervous system (SNS). The most common symptoms include trembling, dyspnea (shortness of breath), heart palpitations, chest pain (or chest tightness), hot flashes, cold flashes, burning sensations (particularly in the facial or neck area), sweating, nausea, dizziness (or slight vertigo), light-headedness, hyperventilation, paresthesias (tingling sensations), sensations of choking or smothering, difficulty moving, and derealization. These physical symptoms are interpreted with alarm in people prone to panic attacks. This results in increased anxiety and forms a positive feedback loop.[10]
Often, the onset of shortness of breath and chest pain are the predominant symptoms; the sufferer incorrectly appraises these as signs or symptoms of a heart attack. This can result in the person who is experiencing a panic attack seeking treatment in an emergency room. However, since chest pain and shortness of breath are indeed hallmark symptoms of cardiovascular illnesses, including unstable angina and myocardial infarction (heart attack), especially in a person whose mental health status and heart health status are not known, attributing these pains to simple anxiety and not (also) a physical condition is a diagnosis of exclusion (other conditions must be ruled out first) until an electrocardiogram and a mental health assessment have been carried out.
Panic attacks are distinguished from other forms of anxiety by their intensity and their sudden, episodic nature.[9] They are often experienced in conjunction with anxiety disorders and other psychological conditions, although panic attacks are not necessarily indicative of a mental disorder.
https://en.wikipedia.org/wiki/Panic_attack
This is not hypochondria, or some kind of paranoia or weakness, it's a legitimate neuro-psychological disorder with causes in the nervous system and the mind.
This is actually a pretty common problem, I've had a lot of trouble with it myself, and it's a huge pain precisely because the symptoms (in addition to being terrifying and immensely unpleasant in themselves) do so closely match those of a heart attack/stroke. It's hard to get around the concept that a psychological problem can cause such intense physical reactions, but it's absolutely possible.
It's true that there could well be an accompanying cardiac problem, I'm not writing that off, and nothing can rule that out except a thorough investigation by a cardiologist (and I think Foreigner gave some great advice about seeking medical attention on that from), but whether or not there is a heart problem, it sounds like there's definitely an anxiety problem.
I'd recommend reading up on anxiety, especially panic attacks and panic disorder, and looking at the symptoms and whether they match your experience. It gets a lot easier once you realize that what you're experiencing is a recognized disorder and that tens of thousands of people experience the same terrifying symptoms.
I don't have much advice to offer on the cardiovascular front except to repeat Foreigner's advice to see a doctor, and until then there's not a lot you can do on that level. But you can address the anxiety side of it, which will help you whether your problem is pure anxiety or a combination of anxiety and a cardiac issue.
CBT and mindfulness training have both demonstrated incredible benefits for anxiety disorders, since they allow you to recognize the symptoms of the anxiety before they spiral out of control, to acknowledge them as what they are before the feedback loop kicks in. Meditation, particularly different breathing techniques, has helped me immensely.
Talk therapy is a good idea also. It's a long term process, but if you're experiencing these kinds of reactions to stimulants then you're possibly pretty highly strung to begin with, and having someone to talk to and figure out what in your life is causing you stress and how to deal with it can make a huge difference. Even just having someone to bitch about your life to without having to hold back can be beneficial.
Lifestyle changes can make a huge difference - cut off any stimulating drugs (including marijuana and psychedelics), ideally stop or cut back on alcohol and tobacco as well. But the drugs in particular have to go, at least for now, if you don't come to terms with that then you'll just keep setting off episodes and worsening the problem.
Look at improving your diet and sleep pattern. Do some light exercise if you feel up to it, once you've been cleared by the cardiologist.
As far as medication goes, I haven't had much luck with SSRI's or similar, but some people apparently do, so it might be worth a shot. If you can find a doctor willing to prescribe benzos and you feel you can avoid abusing or becoming dependent on them (benzo addiction is fucking awful), then having some on hand to head off an episode a couple times a week can be incredibly beneficial. Just knowing that you have the medication on you and can stop the symptoms is often enough to help you stay calm. On the flip side, it's very easy to become addicted if you take them on a daily basis, so be careful with that.
I also found propranolol incredibly beneficial in low doses. 10mg 2 or 3 times a day will keep your blood pressure and heart rate from jumping as high and will bring them down faster when they do, and it doesn't have the addictive potential of benzos or the side effect profile of SSRI's (although don't take it, or any beta blocker, if you still use stimulant drugs, as the combination is dangerous).
Anyway, good luck. I've been more or less right where you are (experiencing severe anxiety around symptoms which feel like cardiac problems after abusing MDMA and meth), and I know how it feels, but you can recover if you're willing to make the changes necessary.
