What depression can involve
Depression flattens things. Not only mood, but energy, interest, sleep, appetite and the ability to hold a thought long enough to finish it. One of its quieter cruelties is that it edits memory: in the middle of a low stretch it's genuinely hard to believe there were better weeks, and equally hard to describe how long this one has gone on.
That's the narrow thing a record can do. Not fix anything, and not stand in for treatment or support, but keep an account that doesn't depend on how today feels. A few weeks written down, even a word on the worst days, is something to read back and something to bring to an appointment.