Are your legs aching from using the treadmill? It would be very unlucky to have a clot in both legs at the same time.
I got lost somewhere, usually they give you an IV to keep you hydrated and inject the Thallium right there (meaning eg. in the wrist but not in the leg) and/or the medication to get your heart going if you can't take the treadmill. Are you saying this is not what happened?
Please go to the ER ASAP this could be a blood clot....Call 911 to transport...