I believe most heart murmur conditions are caused by a leaky valve or chamber wall. In the case of the wall, I think that is the type murmur that people can "grow out of", i.e., as the child grows the heart leakage grows shut.
I have never seen anyone comment on physical trauma causing a heart murmur. I would guess there is no correlation to the accident you describe and you having a murmur.
Mitral Valve Prolapse (Heart Murmur) is a valve defect. When it is found when your young doctors tell you that it is possible that you will grow out of it because your heart is most active at that time. Basically what Jerry expalined.
It is not caused by trauma and rarely do you grow out of it. Mine was detected at age 16 and i still have it 30 years later.
After a trauma, blood pressure WILL be go up except in the event of shock in which case it will plummet. As the blood is surging more than usual from the adrenaline, your barely audible any more murmur is more detectable. The tauma only causes a murmur in the event of some serious cardiac trauma . Once your over the fight or flight response to it, both your bp and your murmur should return to their baseline. Glad you are ok.