Oh I am so sorry god bless you! I can't answer this. But I can relate! I have the same problem and its like no one understands. Its random and its sudden. I can be sitting, standing or walking. Doesn't matter. I have been doing this for 2 months now. I can't see a cardiologist till sept 13. I did wear a event monitor for 30 days. I've had many ER visits. It is scary. I hope they figure it out and good luck to you.
The difference between Sinus tachycardia and Atrial Tachycardia is that Sinus is a normal heart beat that may be fast while PAT is a tachycardia that can be caused by a physical problem with the heart causing the heart to beat fast. The best way to tell if it is normal or atrial is if it starts and stops in what feels like one beat. That would be an indication of an arrhythmia as opposed to it just being a fast beat triggered by dehydration or nerves or something like that even something outside the heart. My type of SVT, which was AVNRT, was really an atrial tachycardia. The term PAT means paroxysmal atrial tachycardia where paroxysmal means it comes and goes. PSVT or paroxysmal supra-ventricular tachycadia or a tachycardia occurring over the ventricles meaning in the atria is another term for PAT and is caused by extra muscle fibers in the heart allowing the heart beat to get caught in a reentry loop. This said, a run of pacs can also be termed PAT so it would need to be diagnosed if you do indeed have PAT, likely by determining if it starts and stops abruptly and if it is a run of pacs or just a fast heart beat that is caught in a loop.
The fact that yours comes down slowly may mean that you are having an autonomic nervous system response to the skipping beats where the brain over reacts to the skipping thinking the heart is beating too slow or something so it speeds up to compensate. Once the brain knows the coast is clear so to speak it slows down or maybe the adrenaline that is kicked in to speed up the heart rate dissipates but a slow reduction of rate isn't likely to be a reentry type of tachycardia. Unfortunately that also means it isn't easily fixable either. So how long does it stay elevated? Have you tried vasovagal maneuvers to slow it down if it doesn't slow down within a short duration? Try holding your breath while bearing down like straining to go to the bathroom or drink a very cold glass of water and see if that helps slow it down. Definitely try and slow your breathing by taking deep breaths and see if it helps.
One interesting side note is that many tachycardias are triggered by premature beats or that skipped beat feeling. I had no clue that I had two different types of arrhythmia, an svt and premature beats. It was a perfectly timed premature or pattern of premature beats that would give the heart beat signal a chance to form a loop around my avnode causing a heart beat well into the 200s. It would start and stop on a dime and feel crazy manic fast. When it was caught it was running at 230. I had an ablation to correct the svt but I am still left with premature beats. I do believe I sometimes get short runs of pacs but have not had an svt/tachycardia episode since the ablation.
This all said, most cardiologist would not deem tachycardia originating from the atria serious. I personally think they maybe should take them more seriously but they are not considered a major health threat unless the beat remains elevated for long periods of time. The going theory is that we really don't totally need our atria. The ventricles are vital but people have lived for years on end with the atria failing or what is called fibrillating or quivering when a person is in permanent afib. So to term the issue serious may cause the patient undue worry. It is best to get on top of what it is and manage it as best as possible for the long term health of the heart but try to be safe in knowing that odds are what is going on is something you will be able to live with.