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 or go to an emergency department if you have a suicide plan, intend to act, have already harmed yourself, or cannot stay safe.
If possible, remain with someone you trust and move away from anything you could use to hurt yourself.
Seek prompt medical advice if symptoms become more severe, continue throughout the month, or change after starting a medicine or hormonal contraceptive.
New periods of unusually high energy, very little need for sleep, impulsive behaviour, or racing thoughts also need assessment because they may suggest another mood condition.
Get same-day urgent help if you are having thoughts of self-harm or suicide, even if you do not intend to act on them.
Arrange a routine appointment if symptoms repeatedly appear before periods and affect work, relationships, education, sleep, or daily activities.
Bring a symptom diary if you have one, but do not delay seeking help simply because you have not completed two months of tracking.
Every sign above is quoted from the sofidex article on Premenstrual dysphoric disorder. If you are not sure, err upward — it is always reasonable to be checked.