Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Contact emergency services or a local crisis service if you may act on these thoughts.
A sudden, severe headache with vision loss, double vision, confusion, fainting, or repeated vomiting needs emergency assessment, regardless of changes in sex drive.
These symptoms can occasionally signal a serious problem affecting the brain or pituitary gland.
Seek urgent help if low desire occurs with thoughts of harming yourself or suicide.
Book a routine appointment if low sex drive lasts for several weeks or months, causes distress, affects a relationship, or follows a change in medication.
You should also arrange an appointment if you have pain during sex, vaginal dryness, erection changes, missed or irregular periods, nipple discharge when not breastfeeding, or symptoms of depression.
The article also says
If sexual activity involves pressure, threats, or fear, seek support from a trusted healthcare professional or local domestic or sexual violence service.
Every sign above is quoted from the sofidex article on Low sex drive. If you are not sure, err upward — it is always reasonable to be checked.