I've had moments like that
years ago I used to have a Toyota camry and decided to change the discs and pads myself.
After removing the caliper, I thought the centre hubnut was holding the disk on - first I didn't have a large enough socket - so bought one - after trying all I could the nut would not budge - even with 2 of us pushing down on a metre long steel pole - in the end it turned out there was nothing holding the disc on - even the screw which should of been there was missing and all that was needed was a tap and it fell off !!!