It's good that he's not in pain, hopefully by the time they figure out whats wrong it's fixed itself. Could you give Rakins activities to do lying down. Maybe some puzzles and kongs that don't require him to walk around/stand so he stays quite but has something to do. Maybe puzzles that only require him to use his front paws. Like cutting some tennis balls in half and putting them in a muffin tray with treats under each so that he has to get them out of the tray to get the treats, he could do it lying down or sitting then to minimise the stress on his back end. Does he like to chew? if so maybe some new chew toys are in order. When Holly was speyed she did a lot of chewing, it was amazing how many chew toys she got through in just a couple of days. She couldn't be too active (it hurt) so I think the chewing helped her deal with being bored, used up energy and probably helped her deal with the pain. If Rakins doesn't like to chew plastic nylabones (Holly does but I know a lot of dogs don't) then there are some more natural alternative such as deer antlers (although I think I remember you saying you couldn't get those) or just flavoured ice cubes or cow hooves. Holly recently had a cows hoof (the petshop gave it to us for free for Holly to review , but they retail for about $2.50 here so pretty cheap and should last at least three days) and she loved it. Or maybe just a raw carrot if Rakins likes them. Maybe ask your vet what sort of thing would be most appropriate considering that lump and the vomiting.