An attack of anxiety or fear which triggers the body's fight/flight response.
This can give rise to a number of unpleaseant physichal and mental symptoms.
Contarary to some belief, medication is not needed to "cure" panic attacks.
They stop when you stop trying to fight them and just accept them and patiently wait for them to end.
Also a healthy diet, excercise and thinking about other people/things and not yourself helps greatly. Another thing that helps if you practice it is observing your feelings and not engaging with them.
"Why is she freaking out about every little thing and why does she think she has a brain tumor/heart attack"
"Shes having a panic attack"
"hey man how are your panic attacks?"
"I don't get them anymore, I realised I was just making them worse by worrying about them and trying to fight them, when I stopped doing that and started accepting them they went away in a month"