Yes they do. Between 2x4's, steel beams, flying KO's, gas pipes, uh, what else? Tooo many times i have walloped myself. I already know my hands are going to be toast by retirement, but hope my brain will be intact lol.
I lost 4yrs of my life due to a head injury. Cool part is I don't remember most of it...lol! Though the titanium plate in my neck serves as a reminder.