Most people start a symptom log by deciding to write in it when something happens. It is the obvious approach and it produces a record that is much weaker than the effort put into it.
The better rule is duller: write something every day, even when there is nothing to say. Ten seconds on a quiet day is worth more than it sounds, and the reason is not effort or discipline. It is that a log with only bad days in it cannot answer the question everyone will ask of it.
Why bad days alone do not show frequency
Say your log has fifteen entries in March, all of them difficult days.
That is either a month where you were unwell half the time, or a month where you were unwell half the time that you wrote anything down, and nobody reading it can tell which. The fifteen entries look identical in both cases. The information that separates them is the sixteen days you did not write, and those days are invisible.
Now say your log has thirty-one entries in March, sixteen of which say some version of "ordinary day, a bit stiff in the morning." The same fifteen bad days now sit inside a complete month, and they mean something specific: this happened roughly every other day. That is frequency, and it is a fact you cannot reconstruct later.
The quiet entries are not filler. They are the denominator.
What a gap actually looks like from outside
This is the part worth understanding properly, because it is the thing people are most surprised by.
Suppose your log runs steadily through spring and then stops for three weeks in June before picking up again. To you, that gap has a reason. Maybe you were doing well. Maybe you were doing so badly that writing anything felt impossible. Maybe you were travelling, or lost the habit, or your phone broke.
To anyone reading the log, all of those look the same. The record does not say. And the two most likely explanations point in exactly opposite directions: a good stretch, or the worst stretch in the whole document.
That ambiguity is not something you can clear up afterwards by remembering. It is a hole in the record, and holes in a record tend to get read in whichever way requires the least effort.
The fix is not to write more on bad days. It is to write something on every day, so that a gap becomes rare enough to be meaningful when it does happen.
Do not backfill
When people notice a gap, the instinct is to fill it in from memory. Do not.
Reconstructed entries are guesses wearing the costume of records, and the guessing gets worse the further back it goes. Severity flattens, durations round off, and the small functional details — the ones doing the real work — are simply gone. Worse, a run of entries written in one sitting tends to look like a run of entries written in one sitting.
Close a gap honestly instead. Write one entry, dated today, that says what happened:
June 24 — Nothing written for the last three weeks. Two rough patches in there that I did not record at the time, and I do not trust my memory of the details well enough to write them now. Starting again from today.
That is an honest document. Three weeks of invented entries is not, and the difference matters more than the missing detail does.
The ten-second entry
Daily only works if a quiet day genuinely costs nothing. Set the bar low enough that you will clear it on a bad night.
April 8 — Ordinary day. Some stiffness first thing, gone by mid-morning. Nothing else.
That is a complete entry. It has a date, a description, and an implicit severity. Written on ninety days like it, that same sentence turns your bad days from a list of complaints into a pattern with edges.
If ten seconds is still too much on a given evening, write four words. A dated line saying "ordinary day, nothing much" beats a blank.
Consistency beats completeness
Given a choice between one thorough entry a week and a short entry every day, take the short entries.
A weekly summary is a memory exercise, and it flattens exactly the detail that makes a record useful. Frequency disappears into "a few times." Duration becomes "a while." The particular Tuesday you left work early becomes "I missed some work that week."
Nobody needs your log to be well written. It needs to be dated and it needs to be regular.
Things you only see with daily logging
There is a second payoff that has nothing to do with paperwork.
A record with entries on the quiet days shows patterns that bad-day-only records cannot. Symptoms that cluster after short sleep. A build-up over three or four days rather than something that arrives out of nowhere. Weather, a change in routine, a particular kind of week at work. Whether things are slowly getting worse across a year, or holding steady, or better in one season.
None of that is visible in a list of the fifteen worst days. It shows up in the shape of the whole thing, and the shape only exists if you filled it in.
That is worth having for your own sake, separately from any claim. It is also the kind of thing that is genuinely useful to say out loud to a doctor, because it is a pattern you observed rather than a symptom you remembered.
If your log is already patchy
Do not start over. A patchy record that goes back eighteen months is more valuable than a perfect one that starts today, and restarting throws away the only thing you cannot buy back, which is elapsed time.
Keep what you have, note the gaps honestly if there are big ones, and start writing daily from now. Six months from now the recent stretch will be dense and regular, and the older patchy part will still be doing its job as evidence that this has been going on a long time.
The short version
Write every day, even when nothing happened. Quiet days are the denominator that turns bad days into a frequency. A gap is ambiguous from the outside and cannot be repaired from memory, so close one honestly rather than backfilling it. Ten seconds is a complete entry. Consistency beats completeness, every time.