Two failure modes, and both are common. One is sitting on a symptom for a year because it seemed too small to mention. The other is a month of researching at 2am about something that turns out to be an antihistamine and five hours of sleep.
The way out of both is knowing which features actually change the clinical picture.
None of this replaces assessment. It is the list of things worth saying out loud, and the small set that should not wait.
Immediate — today, not an appointment
Contact emergency services if any of these are new:
- Sudden change in thinking, speech or comprehension, over minutes to hours.
- Weakness or numbness on one side, facial droop, difficulty speaking or understanding — possible stroke, and time matters enormously.
- Sudden severe headache, particularly the worst you have had.
- Confusion with fever, neck stiffness, or a new rash.
- Confusion developing over hours to days, particularly in an older person or someone recently unwell or started on a new medication. This is delirium and it has causes that need finding now.
- Thoughts of harming yourself. Local emergency number, or in the US call or text 988.
- Cognitive change after a head injury, especially with vomiting, drowsiness or worsening headache.
Prompt — an appointment in days to weeks, not "see how it goes"
- Clear progression. Worse than three months ago, worse again than six. Progressive is the single most important feature.
- Others have noticed, and are raising it unprompted. This carries more weight than self-report.
- Language is affected — not occasional words, but consistent difficulty producing or understanding speech.
- Getting lost in familiar places, or difficulty with routes you know.
- Difficulty with familiar practical tasks — operating something you have used for years, managing money you have always managed.
- Personality or behaviour change noted by others: apathy, disinhibition, loss of interest in people.
- Focal neurological symptoms: persistent numbness or weakness, visual changes, difficulty walking, new clumsiness on one side.
- New headaches with the cognitive change, particularly if worse in the morning or on coughing.
- Any of this under fifty with clear progression.
- A family history of early-onset dementia or a known genetic condition, with new symptoms.
Worth raising, not alarming
These deserve a proper look and are much more often something mundane:
- Fog that began after an illness
- Fog that began within a couple of months of a new medication
- Fog alongside snoring, unrefreshing sleep, or daytime sleepiness
- Fog with fatigue, weight change, temperature intolerance, hair or skin change — the thyroid pattern
- Fog with heavy periods or a restricted diet — the iron and B12 pattern
- Fog alongside low mood, loss of interest, or anxiety
- Fog around perimenopause
- Fog that is clearly worse in the afternoons and better after rest
- Fog that has been stable for years and is not progressing
Most of this list resolves into something identifiable and treatable. That is the usual outcome, and it is worth knowing before the appointment.
The features that are reassuring
Not a guarantee, and not a reason to skip an appointment — but worth knowing, because they describe the great majority of fog:
- Stable rather than progressive. The same for a year or more.
- Fluctuating with obvious causes — better after a good night's sleep, worse when stressed or busy.
- Nobody else has noticed.
- Memory for events is intact. Forgetting where you put things while remembering conversations from last week is a very different pattern from forgetting the conversations.
- Insight is preserved. Being worried about your own cognition is, in itself, somewhat reassuring; the conditions people fear most tend to reduce awareness of the problem rather than heighten it.
- A plausible contributor is present and untreated — bad sleep, a sedating medication, high stress, low iron.
What a reasonable workup includes
If you are being assessed, some version of:
- A history, which is most of it: time course, specific symptoms, what else changed, family history.
- A medication review, the whole list including supplements and over-the-counter.
- Sleep, in detail, including snoring and whether you wake refreshed.
- Mood and anxiety screening.
- Blood tests: thyroid function, full blood count, B12 and folate, iron studies, glucose, kidney and liver function, calcium. Sometimes more depending on the picture.
- A brief cognitive screen, which is a screen and not a diagnosis.
- An examination, which is one of the things needing a room.
- Further investigation if indicated: imaging, sleep study, formal neuropsychological testing, specialist referral.
If your assessment covered none of the blood tests and did not include your medication list or your sleep, the common causes were not excluded.
The question to end on
If watching and waiting is proposed — often reasonable — ask one thing: "what would make you want to see me sooner?"
It converts an open-ended wait into something with a boundary, gives you a specific list to watch for, and is also permission to stop monitoring everything else.