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 if your baby is very difficult to wake, becomes limp or unresponsive, has a seizure, struggles to breathe, or develops blue, grey, or markedly mottled skin.
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
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Arrange same-day medical advice if the fontanelle is clearly sunken and your baby has one or more of these signs:
Much fewer wet nappies than usual
A dry or sticky mouth, or few tears when crying
Repeated vomiting or frequent watery diarrhoea
Refusing feeds or being unable to keep feeds down
Unusual sleepiness, weakness, or persistent irritability
Eyes that also appear sunken
Fever in a baby younger than 3 months
3
Does any of this apply?
Book an appointment
A routine appointment is appropriate if the fontanelle continues to look sunken despite normal feeding, wet nappies, and behaviour.
Also book an appointment if you have concerns about feeding, growth, or weight gain.
Every sign above is quoted from the sofidex article on Fontanelles - sunken. If you are not sure, err upward — it is always reasonable to be checked.