Oh Doodle. How simply awful for him. Such an easy thing to do but falling on your back on stair edges is going to take some time to recover from. Once he (and you) are over the shock, try to ensure he’s a good patient. Assuming he has broken ribs? Or strained, twisted or bruised lots, he does need to keep on top of the painkillers and try to do very little. If he feels despairing, he should try to hold on to the thought that he did it and it was a simple accident, he’s not ill and so mustn’t worry - that pain will go. Meanwhile take regular painkillers and not wait until he’s desperate. Wishing him everything for a rapid recovery. And you, please take care of yourself as well. Rest both of you. I’m so sorry. ?