Welcome Allalone: I't sounds like a tough situation with your son, I'm so sorry. Did he get a diagnosis, when he was hospitalized? I'm guessing that since he was taken to the mental hospital by police, he probably isn't cooperating with any treatment, is that the case?
To the right of this post, you will find links to some useful information and communication tools that could help.
I don't know what to do - I feel sick all the time with worry - both about him and about the next time he will blow and hurt someone .
Aside from the damage your son could do by driving under the influence, are you concerned that he may become violent with someone?
What would you like to see happen with your son right now? Go to therapy? Go to a facility for substance abuse, or go to a residential facility for BPD?
Are you able to get some therapy for yourself? Do you have family or friends that are supportive?