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 severe trouble breathing, swelling of the tongue or throat, faintness, confusion, blue or grey lips, or a rapidly developing reaction involving more than one part of the body.
If you have been prescribed an adrenaline auto-injector, use it as directed while emergency help is arranged.
And for anyone, someone who:
Seek prompt medical advice if you develop new wheezing, chest tightness, shortness of breath, or a cough that wakes you at night.
If you already have asthma, get urgent help when symptoms are worsening or your reliever medicine is not working as expected.
Arrange routine medical advice if your symptoms keep returning, interfere with sleep or daily activities, or remain troublesome despite correctly used non-prescription treatment.
An assessment is also useful if the diagnosis is uncertain, medicines cause side effects, or you want to discuss allergy testing or immunotherapy.
Every sign above is quoted from the sofidex article on Grass allergy. If you are not sure, err upward — it is always reasonable to be checked.