I once had a chest infection that migrated up to my mouth. My gums were, like, black? It was gross. And I could not eat at all because I had no sense of taste and nothing was appetising. I was only about 11, so my mother freaked, but I survived. You probably need to be a bit more careful, depending on how much weight you lost in Japan, so drink a lot of fluids including calorific ones like fruit juice. Smoothies and other blended drinks would help, and ice cream will be soothing but also delicious.