The mom in me wants to run and hug him but I'm not sure that is the best thing.
Sounds like a plan if that is how you feel when you arrive
When my daughter was in rehab I tended to leave the direction to her. I tried not to suffocate her with my anxiety or ask so what do you do each day, how do you feel...are you craving, etc. etc. I found that letting her know I really missed her and I thought she looked great and giving her a big old hug was all that was needed to break the tension and get into the "normal" mom/daughter conversation. We talked about everything...whatever came to mind. I didn't focus on what she was there for; if she wanted to tell me about it, she would volunteer the info. And actually she did..This was what she was living day in and day out, so it naturally came up. One time she had a half day pass and we went out and just did fun things she wanted to do. That is a day that stands out in my memory as a beuatiful, happy time.
As far as his progress, it helped me to remember that just like us, our addicted loved ones progress in their own time and in their own way. I can relate to that feeling of wanting to get a "good report." I kinda felt like it was parent teacher conference and I had hopes of hearing she was straight A's. One thing I heard more than once from counselors in rehab is that they could not predict who was going to stay the path and who would relapse. They saw the model client use within hours of leaving and the ones they thought just didn't get it struggle through until suddenly something clicked and they worked recovery for the rest of their lives.
I hope you can let go of the fears and worries since there really isn't anything we can do to change things, and enjoy the visit with your son. Hugs