Sparrowhawk nice photo
Same thing happened to me years ago, just stopped for a break and sat in a chair on the patio, as I stood up sparrow hawk skimmed my head and shot into the bushes in front of me, problem was there was a brick wall right behind the bushes, sparrow hawk appeared, groggily, shook it’s head and flew off.A sparrow hawk bounced off my head a few days ago! I was outside the van bending over the laundry when I heard a squawking noise and as I stood up a small bird flew into the large bush next to the van followed by another bird clipping my hat. There was a commotion in the bush then the sparrow hawk exited and flew off. Seen it about a couple of times since then though it hasn't assaulted me again .
Have a look at this, fantastic film on a garden sparrow hawk.
Oh by the way, their is bugger all you can do to stop them.