Thanks. Turns out I had a flat tyre, in a remote area with no cell phone coverage. I thought I totally had it under control... unloaded the car, took out the emergency wheel, jacked up the car etc.... but the nuts had been put on with a pneumatic drill and I was unable to budge them no matter how hard I tried.
I had to flag down help. Got it all sorted and drove the remaining two hours very cautiously on my emergency wheel.