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 if someone suddenly cannot read, speak, understand language, or use one side of the body normally.
These can be signs of a stroke or another acute brain problem.
Get emergency help if someone is at immediate risk of self-harm or suicide.
This is not a direct symptom of dyslexia, but distress related to school, work, or bullying should always be taken seriously.
Seek prompt mental health support if reading difficulties are linked with ongoing anxiety, school refusal, marked loss of confidence, or depression.
Arrange routine help when a child has persistent difficulty learning letter sounds, sounding out words, reading fluently, or spelling despite appropriate teaching.
A teacher, school learning-support service, primary care professional, or relevant assessment service can help identify the next step.
Adults may seek a routine assessment if reading and writing difficulties interfere with study, work, forms, finances, or other daily tasks.
An assessment can also identify whether attention, language, hearing, or vision problems are contributing.
The article also says
Dyslexia develops gradually; it does not cause a sudden loss of reading ability.
Every sign above is quoted from the sofidex article on Dyslexia. If you are not sure, err upward — it is always reasonable to be checked.