Just an update. He was 3, had been well until very recently when sudden weight loss despite eating followed by sharp deterioration. Despite drip, antibiotics, etc at Vets he continued to deteriorate and was PTS this morning. The Vet (who has 5 rabbits of his own) suspects an injury as he was off his legs and renal and liver blood tests not too bad. Although also had an infection including some fly maggots caught very early (no destruction) on board he feels this may have been opportunistic rather than the underlying cause. My poor bunny, his partner looks so puzzled and alone.