"The worst thing is that they come out of nowhere"
This is not true, and makes people that have this issue helpless, and thus flames on their situation.
It has been proven by David Barlow(the foremost expert on anxiety) that panic attacks have internal or external cues. IE: increased HR, or traffic on highway, that sends initial symptoms, and here is were we have control and why panic attacks are not out of the blue.
If you react to the initial symptoms, with thoughts like OMG i am going to die, further adrenaline with be released, then you will panic.
However, if you react by saying, oh well my hr is up, that's ok, its healthy for my heart to beat fast , like exercise, panic will stop.!