Thanks for your question on HCM.
In my opinion you are having
musculoskeletal pain.
End of chest bone,
xiphoid process gives attachment to many muscles like abdominal, diaphragm, intercostal , pectoralis etc.
So
tendinitis of any muscle can cause pain at xiphoid process.
Since your all other work up is normal, I think it is musculoskeletal pain only.
Try to follow these steps for better symptomatic relief.
1. Avoid heavy weight lifting and strenuous exercise.
2. Avoid bad postures in sleep.
3. Avoid movement s causing pain.
4. Take good painkiller and
muscle relaxant.
5. Apply warm water pad on affected site.
6. Loose weight if you are
obese.