The symptoms showed up late last year, not long after my 71st birthday. A weariness settled in. It muffled my normally robust energy, leaving me bored and brittle. Day after day I consulted the list I had thoughtfully prepared outlining tasks I’d always planned to tackle when I retired: Sort through old photos Clean up gardening supplies in the garage Cull holiday decorations in the attic List armchair on Craigslist Good, legitimate goals, all of them—the kind of unfinished b