what exactly is a panic attack?

I just want to make sure I'm on the same page as everyone else here when I talk about panic attacks. Thanks.

I experience racing heart, difficulty breathing, tightness in my chest, excessive sweating, dizziness, and an overall feeling of unease - like something really bad is about to happen and I have to brace myself for it. Others may experience it differently.

I think this is quite a good description:

http://www.medicinenet.com/panic_disorder/article.htm

For me, it first comes in as a wave of extreme irritability. I feel like I want to scream, punch the wall, break something; when I feel it coming on, I lock myself away, I move to a private place (ie. my bedroom, a bathroom stall, my car). I breathing starts to quicken, my legs are bouncing, I begin biting my nails, or clenching my hands into fists...sometimes, I dig my nails into my skin. My stomach begins to burn like you would not believe, I feel nauseated, like I am about to pop. And when I get to the point to where it feels like I am about to pass out, I cry...and I mean CRY. After that, it's gone, like nothing happened.

Agitation, heart races ,hands go numb feel like 'im going to pass out altho I never do ummmm feeling that something awful is going to happen any minute now.

For me I end up pacing my room and my breathe becomes shallow. I also end up hitting myself in my head, but not really hard, more like a tapping. I have no idea why I do that. It is really weird.

I had a panic attack which caused me to not be able to inhale and I was trying to catch my breath and calm myself down; I thought I was dying and would dive into the carpet before reaching my cell phone; I think these attacks can also be spiritual, as I've never had one before and an immediate one month trial on a heart holter monitor did not reveal any heart problems. Drs. don't know the cause, even a psychiatrist; I think I know what it was but is too controversial, even, to post. 'certainly do hope it never happens again because it was very terrifying to think you are dying and can't help it.