Brew, I did something similar about 20 years ago when I was still working. I always cut my own hair and this particular time I was using the electric clippers on the lower back part of my head. I had attached a number 6 ,guard’ on the clippers, at least I THOUGHT I’d attached it securely but it came off without warning and dropped on the floor. I obviously stopped straightaway but there was now a small shaved area on the back of my head. I used an eyebrow pencil to colour on to my scalp - I was dark haired then - and luckily I had enough hair on the top and sides to back comb over the bar