When i were a about 10 years old i nicked off on a friends bike, i turned around to see him chasing me and as i faced forward......WHAM.....i hit my head on a low bar and knocked myself unconscious as well as cutting my head wide open
I also stood on a chair when i were unwell to get paracetamol from a high shelf, i promptly passed out hitting my head on the way down, i awoke to find myself with my husband standing over me asking what i were doing lying on the floor, and when i sat up i realised i were lying in a pool of blood (i'd hit my head again!)
I also got inspiration from a cartoon where you make a seesaw from a plank of wood and a brick, i put an old slate on one side and jumped on the other, i looked up to see where it were and i couldn't see it, so i walked back about 10 meters to my back door and it came down and hit me on the head...... i got hit on the head a lot!