Yesterday morning I found a bumblebee crawling around in the bedroom. I caught it in a container and put it outside in the sun on a Pulmonaria. When I looked 10 minutes later it hadn't moved at all. I remember reading somewhere on here that sugar water or honey could help.
As soon as I placed a drop of honey on the flower directly in front of the bee it immediately started to eat it and within 15 minutes had taken to the air and was flitting from flower to flower. It made my day.
Many thanks to the person who gave this tip