To OP, my suggestion is to go to your doctor and give him/her a good graphic description of what aikido practice involves. Bring along a laptop and show vid, if possible. Then take his/her advice on what you should be doing. I've had the experience of having a doctor tell me that I could resume "all your normal activity" after a surgery (eye, not back), but when I described the aikido part of my "normal activity", said with eyes bulging, "No! Not that!" So, check it out with your doctor, and make sure your doctor knows what you're talking about.
I had the same experience as Mary. I was cleared to do "anything" up until I showed the doctor a video of me training. We ended up spending a long time going over a lot of things including my warmups. At that point he revised his opinion rather extensively.
Be open and clear with your doctor so he or she can give you an informed reply. My doctor simply never imagined *that* was what we were doing.