Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for new confusion, severe drowsiness, collapse, inability to walk, or abnormal eye movements—especially when the person is undernourished, has been vomiting repeatedly, or drinks alcohol heavily.
Suspected Wernicke encephalopathy needs immediate assessment and thiamine treatment.
Stroke, infection, low blood sugar, head injury, alcohol withdrawal, and other emergencies can look similar.
Seek prompt medical advice after weight-loss surgery if vomiting continues, supplements cannot be kept down, or new numbness, weakness, confusion, or balance problems develop.
Arrange a routine medical appointment for gradually worsening memory, repeated questions, increasing difficulty with daily tasks, persistent poor balance, weight loss, or concerns about nutrition.
These symptoms need assessment but are not usually an emergency when they are stable and longstanding.
The article also says
Do not assume sudden confusion is simply intoxication.
Every sign above is quoted from the sofidex article on Wernicke-korsakoff syndrome. If you are not sure, err upward — it is always reasonable to be checked.