Panic attacks out of the bright blue sky?

Had panic attacks since I was 15... So about 35yr now. Have patiently been waiting for them to become more mild (that's what all the literature showed - getting less as you age).

However, that hasn't been my experience really.

My panic attacks rarely come from stress - during or after. I had a friend almost die a few months ago in front of me (thankfully he's okay now), and I got a little stressed of course - jumped in to help him. But I didn't experience a panic attack that night or for weeks after the event.

Lost my job? Bills piling up? Nope, not a thing.....

I watch my HR on my Apple Watch, and it's typically an ordinary night in front of Netflix, while on the laptop and I'll notice my HR feels a little fast. I'll look at watch and sure enough my resting HR has moved from 65 to 80... then it continues to go up hour after hour until reaches 100 or so. I reach for a Xanax and it calms back down in half hour or so.

After 35ys of this &*(%&*$ problem I still can't figure out why my panic attacks seem to trigger in of non-stressful times? What in the world can surfing the net, doing some work online, or watching Netflix, or just laying in bed listening to an audiobook do to my body to trigger the fight/flight mechanism?

Others experience this too???