I am currently recovering from second concussion in a year's time. I also am a Yin yoga teacher. I have a history of concussion prior to this year's follies. I wanted to respond in case someone else stumbles on this page. I was glad to read Bernie's response, as I have been itchy to return to some practice of any* kind.
What I can tell you from my own experience, and from my personal research is that no two concussions are the same -- even for the same person. The general course of action after concussion is full rest. This is to ensure no pressure to the head and to keep the heart rate low. After that initial time, it's understood to gradually return to activities. I was happy to find this post, because I have been on and off full rest for a month.
If a student/client/friend/self finds any pose returns any* symptoms, they should stop immediately. Any inversions are also contraindicated because of the blood flow to the head. In my case this was an obvious no-no from the pressure in my head. If it is not obvious, I would say wait a month for any inversions like legs up the wall or downward dog.
Personally, I would advise against an open class as the first class back for a general population student. Sometimes reactions to physical movement are wildly unpredictable after concussion. Proprioception,vision, balance can all be affected. How the brain responds to new movement after the fact is tricky.
I hope to share my findings from my personal practice and research with concussion on this forum.
Peace & good health to you