The absolute worst possible feeling a person can ever experience. Period. Basically having a panic attack feels like impending doom even though absolutely nothing can be going wrong in the outside world. Symptoms include, but are certainly not limited to:
Fear of heart stopping
Spinning/Spiraling sensation when you close your eyes
Basically, it just majorly sucks balls to go through a (real) panic attack. Panic attacks are one of the most misunderstood terms in today's vocabulary. Commonly in today's society people will make the statement "I'm having a panic attack because I have so much work/school/other issues to think about", this of course is not true, because someone who is going through a panic attack is literally so scared they can't even speak. It is actually a mental disorder that should be treated immediately because literally NO ONE deserves to feel this shitty.
If I met the man who murdered my grandmother, and had the option of making him experience panic attacks as punishment, I don't think I would. Literally crushing his nuts with 2 bricks would be a less severe punishment