It took about 48 hours, but I finally lost the urge to constantly shake my head. It was as though the antihistamines, steroid injection, and sedative all finally kicked in and I was “in the zone” for an entire day.
The next day, I woke up, shook my head a couple of times, and then the urge was gone (and so was the cone of shame).
I guess that the cause of my head shaking will always be a mystery, but it’s definitely a relief to be back to normal and leave my obsession behind, because it was quite an itchy experience!