The advice I've read is not necessarily to go for a walk outside, but to do something more low-key: wash some dishes, read a book, or simply sit quietly for twe

The advice I've read is not necessarily to go for a walk outside, but to do something more low-key: wash some dishes, read a book, or simply sit quietly for twenty minutes. Especially if you feel "tired" but not "sleepy" -- although these can be hard to distinguish. This is recommended (by expert researchers, on the basis of experiment) as part of a cure for chronic long-term insomnia. Like many cures, it can be a bit arduous at first. I haven't seen it recommended for short-term insomnia, especially when there is some causal factor like starting a new job.