Do you think Tricki was happy to go home? What do you think will happen now?
He wasn't actually ill. There was a lack of proper diet and regular exercise in his lifestyle. The reason of his illness was overfeeding. He was a victim of Mrs. Pumphrey's excessive care. It can be discerned by the fact that Mrs. Pumphrey brought two dozen eggs everyday to build Tricki's strength.
As Tricki is back home again, his mistress would again take excessive care of him and overfeed him. Due to the lack of exercise, he would fall ill again.