WAVERLY, Tenn.—Anna Mays woke up in a panic attack Monday, thinking she was back in the rising floodwater. Two days ago, she had been clinging for her life to the front door of her duplex in rural Tennessee as the water inched up to her neck. Her brother was hanging onto a tree. Then Mays realized where she was: The gym at the Waverly Church of Christ, now her temporary home alongside other victims of record-breaking rain Saturday that sent floodwaters surging through the region, killing at least 21 people. Her story has become a familiar one in Humphreys County, and particularly the small town of Waverly. Large swaths of the community are suddenly displaced, sorting through difficult decisions about what comes next even as they relive the horror of what just happened. “This morning I was having a panic attack and thought I was in water, and I was …