In the show "Castle Rock," one of the main characters was moving between times. In this case, she had dementia, but for the sake of the question, you can imagine you're experiencing real time shifts or might be starting to miss bits. To help herself identify where she was and whether the reality she was experiencing was the real "now," she stashed chess pieces in various places. She knew if she found a chess piece, she was in the present and would become grounded.
If it was you, what might you try to do to ground yourself, identify which time/ reality you were in, or prove that the shifts were happening?