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 an adult or child suddenly loses the ability to read, especially with facial drooping, weakness, confusion, severe headache, or difficulty speaking.
A sudden change may indicate a stroke, head injury, or another acute medical problem.
Get urgent mental health help if someone is at immediate risk of self-harm, talks about suicide, or cannot be kept safe.
Arrange a routine discussion with a teacher, school support service, primary care professional, or qualified learning specialist if reading remains unusually slow or inaccurate despite appropriate teaching.
Assessment is also reasonable when reading or spelling difficulties affect confidence, attendance, education, training, or work.
Seek routine help for persistent anxiety, low mood, sleep problems, or school avoidance, whether or not a reading disorder has been diagnosed.
The article also says
Developmental reading disorder itself is not an emergency.
Every sign above is quoted from the sofidex article on Developmental reading disorder. If you are not sure, err upward — it is always reasonable to be checked.