I've been there, and meds helped me get over the initial hump. Using an exercise heart rate monitor also helped. For me, the thought of heart failure was a trigger for panic attacks. The heart rate monitor allowed me to watch my heart rate rise as I ran harder and fall when I went back to walking. It had an anxiolytic effect. After a few sessions on the treadmill I no longer needed benzos to get through 30 minutes of activity.