We're not doctors here. But it doesn't sound like anxiety. You might have developed anxiety because you're scared of what's happening. Your first experience sounds a bit like what happens the first time you try a cigarette, but I assume you've been smoking them a long time. Don't suppose you thought of getting the cigarettes tested to see if they were just cigarettes -- sounds almost like someone put PCP in them, but usually that happens on purpose to you. Many years ago I smoked some pot and it turned out they had been laced with PCP. Right now you might be feeling what you now expect to feel because of the continuing stress, kind of like PTSD, but that's not what caused the original reactions. You need to find better doctors and figure this out. Peace.
I'm not a medical doctor, but I've been dealing with Anxiety for many years, I feel like an expert. A lot of your symptoms sound Panic Attack related to me. You should read up on anxiety and panic attacks. There are so great videos on the web. The main thing to remember about panic attacks is that they are uncomfortable and scary, but not dangerous. Our nervous system is doing exactly what it was made to do, which is help us, not kill us. Having a fearful reaction to these symptoms can cause the anxiety and panic to return, because we're training our brain that the symptoms are something to be concerned about. Cognitive Behavioral Therapy can be very successful at helping with Panic and anxiety.
If your medical tests keep coming back negative, like all of mine did for years, and you continue to experience this, it wouldn't hurt anything to see a therapist who can help you learn to control your thoughts and feelings when these attacks happen. Retraining your brain to think "okay, this is uncomfortable, and it sucks, but it's not going to kill me, and it will go away," is a really good place to start, after getting some information on what anxiety and panic attacks actually are. Everybody can have very different symptoms, from nausea to tingling, heart palpitations, dizziness, choking sensations, etc etc. My own symptoms changed over the years.
If you feel stuck and aren't getting any firm answers as to why this is happening, I really encourage you to get informed and find a CBT therapist. And just remember, the symptoms are awful, but not dangerous. Our nervous system is there to help us, and keep us alive, not hurt us.