The Day After A Light Workout (walking On A Treadmill)

the day after a light workout (walking on a treadmill) I had stiffness in my heel area the next morning and by the afternoon I could not walk because there was sharp, severe pain in the heel when I walked. The pain is not from putting weight on the heel but occurs when I lift the heel to remove the weight. I immobilized the foot in a walking boot and don't have much discomfort when I walk with the boot on. when the pain occurs it is very isolated in the outside of my right heel. the pain shots up to the ankle. if it doesn't improve in the next day or so I plan to see a podiatrist (I've seen before). Meantime, can you tell me generally what may be happening and what (beyond isolation and rest) I should do?