When I was in high school and worked as a bagger, I was loading groceries into a customer's trunk. I picked up the first bag, turned and... smacked my head into the trunk lid hard.
I was both surprised and staggered. I had to sit for a minute to gather my bearings. As for the customer, she saw the bump and was very concerned for my welfare. "I'm fine, I just need a minute to gather myself."
I had a lump on my forehead for the rest of the shift.
I am a bit of a klutz. OK, I am actually a huge klutz.