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 for symptoms suggesting rapidly rising pressure or sudden brain dysfunction, including:
Reduced alertness, difficulty waking, or loss of consciousness
A first seizure or a seizure lasting longer than expected
Sudden severe headache with vomiting or neurological changes
New inability to stand or walk
Sudden weakness, severe swallowing difficulty, or breathing problems
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
Seek urgent medical assessment for repeated unexplained vomiting, a worsening headache pattern, new double vision, increasing unsteadiness, or marked sleepiness.
These symptoms are especially important if several occur together.
New fever during chemotherapy, problems with a surgical wound, fluid leaking from the wound, or a sudden change in neurological symptoms may need prompt review.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment for persistent but mild problems such as ongoing headaches, gradual balance changes, hearing changes, or unexplained clumsiness.
Most such symptoms are not caused by a tumor, but they still deserve assessment when they continue or worsen.
The article also says
Someone already receiving treatment should use the contact instructions provided by their treatment centre.
Every sign above is quoted from the sofidex article on Posterior fossa tumor. If you are not sure, err upward — it is always reasonable to be checked.