Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Get emergency help now if you have thoughts of suicide or self-harm, feel unable to keep yourself safe, or develop severe confusion or behaviour that is very unlike you.
Chest pain, severe breathing difficulty, or signs of a stroke also require emergency care; these are not expected nicotine withdrawal symptoms.
Contact a clinician promptly if you develop severe or persistent depression, anxiety, agitation, confusion, or sleep problems.
You should also seek assessment for symptoms that are unusual for withdrawal, such as a persistent fever, worsening breathlessness, fainting, or ongoing chest discomfort.
Arrange routine medical or pharmacy support if withdrawal is difficult to manage, previous attempts have repeatedly ended because of symptoms, or you want help choosing a stop-smoking treatment.
It is also sensible to seek advice if you are pregnant, breastfeeding, younger than 18, have seizures, have significant kidney problems, or take medicines that may be affected by stopping smoking.
Every sign above is quoted from the sofidex article on Nicotine withdrawal. If you are not sure, err upward — it is always reasonable to be checked.