Following my running down the slope for about 20 metres, I jammed my right foot against a suitable rock to stop my descent but the momentum caused me to move so far forward that I had to repeat the running and try again approx. 20 metres further down the slope but the result was the same and I had to run again for around 20 metres before a big rock came in sight on to which I could place first my right foot pushing back hard and then swinging round clockwise I placed my left foot higher up the rock to stop the momentum carrying me forward again. Unfortunately this movement caused my rucksack to suddenly swing from right to left, pulling me backwards and in a flash I found falling backwards at about 60 degrees to the fall line and landing hard on my back cracking my head on a rock and then tumbling in a helical fashion for about fifty metres down the rocky slope bashing every part of my exposed body on rocks on the way down. When I came to a stop my nose and head were bleeding profusely. I managed to get the rucksack off and push down past my sweater, fleece, flask and lunch boxes to a box of tissues with which I managed to stem the bleeding. I got my flask out to have a drink of coffee and found it was badly crushed throughout its central section but still managed to get a drink of coffee and get the stopper back in. Looking back I could see my Tilley Hat about 50 to 60 metres up the slope, so I knew that that was were I had first been pulled back off the rock I had stopped on. As it was a very old hat in poor condition I decided not to go back for it but to continue down and work my way eastwards to regain the path down to Llyn Bochlwyd, which I could see well below. I found it difficult to get the rucksack back on so I pushed it down the slope and it rolled for many metres before stopping and I then followed it down sliding on my bottom before pushing it again and repeating the process twice more. This time I found the slope below convex so that I couldn't see what was below so I picked up the rucksack and began to make my way to the right to meet the path but felt very unsteady and after a short way I sat down and had another cup of coffee. I tried again but made little progress before I had to sit again. It was then that I realised that My sun glasses and my phone had been lost at the same time as My hat. I decided to call for help but nobody could hear my call. I got no response. I knew that the sun was beginning to go down behind the ridge and with clear skies it would freeze that night at this height and I was not equipped to spend a night in those conditions. I was about to try again to make my way down, when a young man suddenly appeared about 40 metres away and heading diagonally down the slope about 6 metres below my height. I called out to him to help me. He came over immediately and seeing the bloody state I was in, phoned 999, with the result that the Caernarvon Coastguard Helicopter was called out and it passed us going to pick up the Ogwen Mountain Rescue Team and the returned just as dusk was falling. I was taken to Bangor Hospital and was diagnosed as having a broken nose, cracked breastbone and two cracked vertibrae in my spine. I was discharged 13 days later and soon made a full recovery.