Arming and disarming a door, it's not exactly rocket science
That's the best quote on this thread.
If you were as fatigued as you suggest, you should never have boarded the last sector - you should have offloaded yourself & sought medical advise from your companies local doctor - you have a responsability to yourself, your crew & your passengers to be fit for duty. If you were so fatigued you couldn't correctly disarm a door that actually requires you physically bend down, remove a girt bar & relocate it (i.e. it's not a case of simply moving an incorrect lever) what state would you have been in if you'd actually been required to evacuate an aircraft, fight a fire, give CPR or do a cabin prep?