The manhole lid didn't startle me. It fell and I was left with a foggy feeling and headache. The vibration headaches have been an issue for the last 3.5 years. My 3 year old daughter has tapped me in the head playing around I am left with the same feeling. If say a 1 out of 10 on the force scale. I played hockey and boxing growing up. Have had atleast 5 known conclusions from those sports. Life is great otherwise. I do have safety concerns on the job as I consider that one good knock to the head and I could have major long term problems. My blood pressure is great and I have no problem jogging which is strange because you would think the up and down motion would bring on symptoms. It just seems to be light hits to the head and vibrations will cause me symptoms.