I had a similar accident when I was 19.

I was employeed by a guy who was trying to make a boat into a restaurant (corner of Orams/Browns road and Great South Road).

I was using a big grinder, I must have cut the steel plate too deep and I moved. the blade kicked back, the grinder hit on my jaw and I was knocked out unconscious for like 10-15 seconds. when I woke up I have this massive cut in my mouth. nothing on the face. I was EXTREMELY LUCKY that the blade guard hit my face rather than the blade, I have no scar on my face from where the grinder hit.

after the wound has healed I always have this lump in my neck/jaw area, I didnt pay attention as it doesnt hurt at all, 5 years after the incident one night my neck just swollen, to the size of my head. I cant sleep at all. I went to the A&E, they couldnt do much and sent me home and told me to go to the hospital first thing in the morning, next morning I went to Middlemore and within an hour I was on the operating table.

3 surgeries and countless consultation later they finally discovered the lump I had in my neck was a saliva gland leaking saliva into my neck but my body just absorbed the saliva. the doctor asked if I was in a fight at all or involved in an accident or something hit on my face - then I remembered, the grinder.

now I cant feel part of my jaw/chin/neck area. they have a word for this area - Submandibular. the gland in this area was cut and as result of the operation some nerve were cut as well. I could accidentally cut into myself while shaving without knowing.