Call the scuba-shop and postpone your OWD course.
Yes, of course I did that, even before sending my posting here. Even if I had been crazy enough to consider the possibility of attending (and I'm not), I couldn't move at all. As the doctor foresaw, the pills aren't as effective as the injection, and there's pain all of the time. I cannot move my neck, but even if I don't try, it hurts. But what hurts the most is my arm, then the forearm and wrist, and then the neck. At least it's bearable, not like on the day I went to hospital. I'll go and have some physiotherapy, or osteopahy, or something like that (they do everything at the clinic and I don't know what they'll choose) on Monday, so I expect to improve at least a bit. But in the end, it seems I'm lucky there's no available course for what remains of July and August. I don't know how much this is going to last, but it looks like it's going to be quite a bit.
I've just bought a Cressi Gringo snorkel and a Cressi F1 mask (there's not much to choose from at the local sports shop, so making up my mind was easy) with a view to start practising at home, but you can imagine how poorly I still feel when you hear I don't really feel like trying yet. All I want is to sit down in an armchair and do nothing.