the harm from phentermine occurred in people who took the drug for long periods of time,
and in those cases it was thought to
damage the heart valves--
and that would not cause the pain you are describing, rather requiring special imaging techniques to even find evidence that it has occurred.
The panic attack may have been related, as all stimulants tend to increase anxiety. And during a panic attack almost any symptom can occur, including the things you describe during your panic attacks.