Across a Gold Prairie (2000)

Meet NIPPORI Ayumu, an 80 year-old man, who, due to a serious heart condition, has spent sixty years of his life confined to his house. One morning, he wakes up believing himself to be twenty again. In his mind, he has become the youthful young man that he once was. However, reality fails to keep up with his illusion, and everything around him seems to be quite different from what he is used to. So, he decides that he is simply dreaming. As his reality becomes his dream, his unhappy world turns into a life enriched with happiness and expectations for the future. Ayumu is now enjoying his life to the full again.