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 now if malaise occurs with:
Seek urgent same-day medical advice if you have a fever with a stiff neck, a new unexplained rash, rapidly worsening weakness, or repeated vomiting.
You should also seek prompt help if you cannot keep fluids down, are passing very little urine, or have signs of dehydration such as a very dry mouth and persistent dizziness.
Arrange an appointment sooner if you also have unexplained weight loss, persistent fever, night sweats, swollen glands, ongoing pain, or a major change in appetite.
The article also says
Contact a healthcare professional routinely if malaise lasts longer than about a week, keeps returning, or interferes with work, school, sleep, or daily activities.
People who are pregnant, have a weakened immune system, or have a serious long-term condition may need earlier advice when new symptoms develop.
Every sign above is quoted from the sofidex article on Malaise. If you are not sure, err upward — it is always reasonable to be checked.