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 for difficulty breathing, rapidly worsening weakness, fainting, confusion, or inability to stay awake.
Contact a healthcare professional promptly if you develop possible Zika symptoms after relevant travel, mosquito exposure, or sex with someone who may have been exposed.
Seek urgent medical care for new tingling, increasing muscle weakness, difficulty walking, facial weakness, or trouble swallowing.
These can be signs of Guillain-Barré syndrome.
Severe abdominal pain, repeated vomiting, unusual bleeding, or marked drowsiness also need urgent assessment.
These symptoms are not typical of uncomplicated Zika and may suggest dengue or another illness requiring prompt care.
The article also says
Prompt, non-emergency advice is particularly important if:
You are pregnant or could be pregnant
You are planning a pregnancy after possible exposure
A newborn may have been exposed during pregnancy
Symptoms are worsening or not improving after about a week
Every sign above is quoted from the sofidex article on Zika virus disease. If you are not sure, err upward — it is always reasonable to be checked.