Depression and Concentration
For those of us who suffer from depression, playing lightning chess is a good way to 1) distract ourselves from the pain and 2) measure our concentration level by how many points we lose in our rating over the course of the depression. Mine was fairly severe last month (with added pain from a herniated disk) and I lost over 100 points off my 1200 rating. That's a roughly 8% loss. Measuring concentration is a good way to measure the severity of the depression, of course.