I am also a cardiophobe, and I find what helps me is writing down my symptoms and trying to act like a weather reporter interviewing myself. A weather reporter is an external source observing his or her surroundings, environment, climate, sometimes passing judgment, but usually just telling you what it is going to be that day.
Think of your symptoms as weather patterns, and think of heart attacks, seizures, fainting as an endgame, end-of-world, apocalypic event.
If a weatherman sees clouds, does he automatically assume that there will be an F5 tornado or a worldwide hurricane? What has happened in most cases where there were clouds? - They float on harmlessly and only turn into that F5 tornado 1 out of 10000000000 times. In that 1 time too, there would be other things going on - torrential downpour, strong winds, brownish-green sky, thunder, intense lightning.
Similarly, dizziness - you have stated in your post that you have experienced it numerous times. Have you ever fainted? Have you ever had a heart attack? If not, how could you know that it "feels like [you] are going to have one?" It just is not possible.
My CBT therapist tells me this is what you call a warped thought. A thought that is based off of emotions and not your frontal (logical) cortex of your brain. Feelings are not reality, they represent your body's emotional reaction to external or internal stimuli. In your case, your triggers seem to be hypochondria, fear of a catastrophic medical event. This sets off a chain:
Negative thoughts about harmless symptoms that you have experienced before ----------------> fear ------------------------> Conscious awareness of symptoms and fixation on symptoms ------------------------> more symptoms
The chain repeats itself. Every single time. Sometimes anxiety is brought on out of nowhere, which makes me or you fear that it really is something physical. Again, when these familiar symptoms happen, take a pen and paper out and write it down. Be your own reporter. I'll give you an example:
Thought: I am having a heart attack!
Fear: Crap, I am going to die!
Warped thought: Catastrophizing and fortune telling
More logical explanation: I have experienced these things before and am fine
Anxiety has the potential to bring on any symptom under the sun
I have not had a heart attack so I cannot possibly know how it feels
These symptoms can be caused not only by anxiety but also harmless things like dehydration, stress, fatigue, or just general lethargy
Make sure you write your thought and fear exactly how it comes up in your mind, and make sure you do this DURING the attack. It can be difficult, but it trains your mind to logically think things through before trusting that unreliable emotional part of your brain. Good luck!