Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services now if the person has:
Fainted, collapsed, or become difficult to wake
A seizure
Trouble breathing
Chest pain or a pounding or irregular heartbeat
Severe weakness, confusion, or repeated vomiting
Signs of shock, such as pale, cool skin with marked drowsiness
Keep the plant, packaging, or a photograph available for identification, but do not delay emergency care to collect it.
And for anyone, someone who:
you believe has taken an overdose or swallowed something poisonous
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
2
Is any of this happening?
Be seen today
Contact Poison Control or your local poison information service immediately if anyone may have swallowed lily of the valley, its berries, an herbal product containing it, or water from a container holding the plant.
Do this even if there are no symptoms.
It is not a substitute for urgent assessment of new or worsening symptoms.
3
Does any of this apply?
Book an appointment
Routine follow-up is appropriate after recovery if the treating service recommends repeat heart, kidney, or electrolyte checks.
The article also says
Do not drive someone who is faint, confused, or having heart symptoms.
Every sign above is quoted from the sofidex article on Lily of the valley poisoning. If you are not sure, err upward — it is always reasonable to be checked.