This is a good question for people to respond to. Maybe we can identify with others by reading their responses.
My panic attacks: They started years ago and came out of the blue, with no warning. I called them "puke attacks" since that's all I felt, like I was going to throw up and would immediately retreat to a bathroom if I could. The attacks might have stemmed from a paticular situation that happened.
Now they come out of the blue AND with building anxiety. For instance, I have become very sensitive to smells(anyone else sensitive to them???). So sometimes a certain strong smell(food or something) will make me feel nauseated then panic. I can't really tell the difference between real nausea and panic.
Then there's the panic that comes from anxiety about a situation that has been building up. Like leaving the house and already feeling anxiety and already "what-ifing" before you head out. By the time I'm in a panic attack, it's so hard to think, every little thought seems to make it worse and I can't for the life of me "think" myself out of one. My main symptom is nausea or I guess what I could be experiencing is globus hystericus-tightening in the throat that I take for nausea. I also start to panic after eating sometimes, thinking that I might be sick. I also panic just talking about panicking.
What helped me in the past was being put on xanax(which relieved the globus sensation) and taking time off work and going for walks at the couple parks where I live. It took a year and a half to overcome that first real bad bout with anxiety. Now the xanax doesn't have the same effect but I need to try exercising and going to the parks again. It's cold here right now though so I guess I'd have to bundle up if I want to do that.