I'm sorry you had to go through that today. I understand that kind of anxiety. It does sounds like your son really is pursuing recovery.
Have you tried any meetings for yourself? Al-Anon or Nar-Anon? I only ask because I am positive that I would not have made it through my own son's addiction without my meetings. I experienced true anxiety attacks for the first time in my life. Just knowing others understood and were there for me. I also didn't have anyone in my "real life" that I could confide in. Some days were still tough to make it through but I learned so much there that continues to help me today.