I don't want to seem over the top but I think a checkup
with a cardiologist might be in order.
I worked for 18 years in the mental health field, and
suprizingly alot of the "panic attacks" were related to
mytrial valve prolapse (where the valves in the heart misfunction)
and causes palpitations, lightheadedness, panicy feelings etc.
it may be excersize induced.
One of the things that we teach in diving is
when your feeling panicky (how do you spell that?)
is STOP, BREATH, THINK, ACT. try that when you get
that feeling, just stop what your doing and see if it subsides.
(I'd still get checked out).

Marty