I went to a country boarding school. This happened the year I turned seventeen.
I was on a weekend outing, staying with a friend on their farm. We were out horse riding when I was thrown by my horse and landed very hard and very badly, breaking both wrists and banging my head quite severely even though I was wearing a safety helmet.
I was carted off to the local country hospital, a very small place, where I was x-rayed and had both arms plastered from hand to elbow. Because of the head injury I was told to stay in for observation, although I was pretty much zonked out at the time and went off to sleep pretty quickly.
When I woke up and became re-orientated I realised I needed to go to the bathroom fairly urgently. I got out of bed, wearing my pyjama bottoms and went to the bathroom. I then encountered the problem: I'd need help to clean me up. The nurse who supervised the hospital came into the bathroom and started to wash me down, and, you guessed it, I began to feel an erection coming on.
I was really embarrassed and limped back to my bed and hopped in trying to disguise what had now become a raging hard-on. The nurse simply looked at me, and pulled the sheet up over my waist, leaving me lying there playing one man tent poles. The nurse left the room, and I was presented with the next challenge: how to jack off with both hands imobilised? By now I was desperate for a wank and was rubbing and tugging as much as I could when the nurse walked back into the room. Without saying a word, she closed the door, and walked over to my bed. I should add, I was a seventeen year old healthy and good looking boy; she was about 35 and OK. Still saying nothing, the nurse pushed the sheets down to the bottom of the bed and untied my pyjama bottoms and slipped them from under my bum and moved them right down my legs. I was lying there, effectively naked, with what felt like a monumental erection pointing straight at the ceiling, facing a nurse whom I hadn't spoken to. Silently, she bent over and began to slowly massage my dick. I can't spin this story out because after a few minutes of gentle massage she began pumping me and stroking me, and I came in buckets in a wild orgasm I can still feel. The nurse's medical instincts took over and she promptly cleaned up the mess with a few tissues, pulled my pyjamas up, put the sheet on top of me, and left the room.
I stayed in the hospital two nights and the nurse never mentioned what had happened, nor did she offer to repeat it. By the way, I had a hell of a time learning how to jack off with plastered arms and endured some of the longer masturbation droughts of my life during that period.