That BBC report, while not settling the matter absolutely definitively, seems to pretty much point to that this was most likely a normal loss of car control by a driver trying to push the limits to get a better lap time. Then from the resulting crash receiving a significant concussion from which under medical advice it is deemed safest to ensure no possible impact repeat within a month thus ruling Alonso out of the first race. Given the car was being braked hard up until the point of impact it seems to rule out, pre impact loss of consciousness, seizure or electric shock and honestly some mechanical failure seems unlikely. Hopefully Alonso will suffer no lasting effect and can be back racing by round 2 and we can get back to all talking about the relative performance of the teams/cars.