What a brain dump is, and why it works
A brain dump is exactly what it sounds like: you take everything rattling around in your head and write it down, fast, in one place, without stopping to organise or judge. Tasks, worries, half-formed ideas, the thing you keep meaning to do. It all goes on the page.
It works because your mind is good at having thoughts and bad at holding them. Carrying a running list of everything unfinished is a low-grade, constant effort, the kind that makes you feel tired and scattered without any single cause. Getting it onto the page hands that job to something more reliable than memory, and the relief is immediate, often before you have done anything about the list at all.