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 severe breathing difficulty, chest pain, sudden confusion, or thoughts of harming yourself.
These symptoms are not expected from natural short sleep.
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 help if you sleep very little for several nights and also develop unusually high energy, racing thoughts, severe agitation, impulsive behaviour, or hallucinations.
These are not features of natural short sleep and may signal a mood episode or another health problem.
3
Does any of this apply?
Book an appointment
Arrange a routine medical appointment if your sleep has recently become shorter or if you are not sure that it is refreshing.
It is also reasonable to seek assessment for:
Persistent daytime tiredness or unintended naps
Difficulty concentrating, remembering, or managing emotions
Loud snoring, gasping, or witnessed pauses in breathing
Frequent morning headaches or waking with a dry mouth
Trouble falling asleep despite wanting more sleep
A need for increasing amounts of caffeine or other stimulants
The article also says
If you become sleepy while driving, stop as soon as it is safe and do not continue until you are alert.
Every sign above is quoted from the sofidex article on Natural short sleeper. If you are not sure, err upward — it is always reasonable to be checked.