Nods,
Namaste.
If they have happened often, where? Was there always a 'cold chill'?
If you review each event there may be a 'warning' sign as there are with certain types of seizures.
If you can determine the warning signs, reiki immediately could forestall the full blown event.
Panic attacks, however, often indicate internal struggles.
Reiki all around,
All Blessings,
Firekeeper