You have features of Panic attack
, like sudden fear of Heart attack
other cardiac symptoms and some neurological manifestations like tremor too. Since the various doctors you visited and all the investigations you did ,did not show any significant abnormality your doctors diagnosis of Panic Attacks is likely to be correct. Please do not unduly worry about your previous accident and its not likely to be causing your present problems.
Please take the help of a Psychiatrist
and they will help you decide whether you can be best helped by cognitive behavioral therapy
or medications or both.Its also usual that people with panic attacks visit several doctors because they are so convinced that there is an organic basis to their symptoms.Hope this helps.