To preface this, this isnt the first time its happened. I've been cleared by a cardiologist, but that doesnt make this even slightly less scary.

I wish I could understand this, it could be gastric/hiatal hernia related, but im sitting here and for example this is when it just happened, at this time, my cat goes outside for an hour or two at night, I go check on him till he wants to come in. Im doing something, im not anxious at all actually very distracted and doing well, several times I get up and im just fine, this last time, I stand up, and its like sudden pressure, around the spot of my hiatal hernia..atleast the bottom of my sternum area, and my heart rate skyrockets instantly. Im talking 130-140 bpm, for a couple minutes, freaks me out that it goes that high so of course that adds to it, at a normal time like several minutes before it would only have jumped to 90 or so. After several minutes its still a little fast but probably only 90-95, and the pressure remains. But its just scary when that happens..do everything the same as you have several times in the last few minutes and the last time the heart rate flies off the handle. .
I still feel the pressure, it does feel like I have gas, I did have some dark chocolate 30 to 40 minutes prior and that does seem to set off acid or gas for me, and I dont know if that was the cause or what.

EDIT: Since I typed this its been an additional 30 minutes, my heart rate is up slightly still and I Do have some chest pressure still though its a little better, I just feel awful because this is so scary when it happens. I get a lot of weird chest sensations that I believe is due to my hernia, but I dont understand why it would just skyrocket like that. Its so scary when you do something 9 times, and on the 10th time something like this happens.