I've had them all my life, the first at 21, in my mid 40s now, spent a good 10 years of my life with crippling episodes, were I couldn't go out, drive, and have panic attacks lasting for hours. At the worst, it was so bad, I lost 30 pounds in 1 week, couldn't eat, couldn't sleep with a mind racing 24 hours/day. It's so exhausting for the mind that you start having visual hallucinations, you start thinking about ending your life etc, and then finally, you collapse, what you could call a complete breakdown.

And here's the interesting part, things that you don't necessarily experience till it goes full blown, it's when you reach that point, the end of fear basically, your mind becomes calm. You don't necessarily realize it in the instant but that's it, you've stared into the abyss and it's not as awful as you imagined. At that point, you still have anxiety but that's it, it doesn't control you anymore, you're out of the 2 states loop, panic or fear it may happens. It's still painful, but it's not hell anymore, you know how it's gonna end, there's no more question.

Now, it's an incredible experience, can even become an spiritual one, it did for me, experiencing first hand how reality is subjective and how the mind works.

All in all, I wouldn't trade all those experiences for anything, it gives you an understanding of the human condition that not a lot of things can give you.