Hi dear
every body is different
what is abnormal for one person is perfectly normal for other
a number of systems work together in our body to maintain the blood pressure,as because of accident you
nerve has been damaged therefore your body finds it difficult to maintain a normal blood pressure ,but our body has power of adaptation,slowluy and slowly your body has adapted to the changes caused by nerve damage
as per your query for a normal person lower blood pressure should be above 60mm of hg
but in your case if your body is not having any symptoms like
dizziness ,feeling of impeding doom ,a blood pressure of around 50 is normal
as i said earlier until you are symptomatic yo need not to worry,
any symptom like
palpitation ,gidiness ,feeling of passing out is to be taken seriously ,if you feel any problem it should be a matter of concern
till the time you are asymptomatic dont worry