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 difficulty breathing, throat or tongue swelling, fainting, severe dizziness, or suspected anaphylaxis.
Emergency evaluation is still necessary even if symptoms improve.
And for anyone, someone who:
Seek prompt medical advice for new wheezing, repeated vomiting after a suspected exposure, significant facial swelling, or a worsening reaction.
Use prescribed epinephrine immediately.
Arrange follow-up when symptoms are frequent, interfere with daily life, remain uncontrolled, or have an uncertain trigger.
Evaluation is also important after a reaction to food, medicine, latex, or an insect sting.
The article also says
A clinician or allergy specialist can interpret tests, confirm necessary avoidance, update medical records, and provide a written action plan.
People prescribed epinephrine should periodically review injection technique and check the device’s expiration date and condition.
Medicine allergies may be reassessed because some labels can be removed after appropriate testing or a supervised challenge.
Children with certain food allergies may need periodic evaluation because some allergies resolve over time.
Every sign above is quoted from the sofidex article on Allergies. If you are not sure, err upward — it is always reasonable to be checked.