If you’re unfortunate enough to catch the flu, chances are you’ll be able to take care of yourself at home.

But our immune systems become weaker as the years pass. That means we often need to seek treatment sooner than we might have when we were a little younger.

After all, the flu can become severe⁽¹⁾. It can even result in pneumonia or inflammation of the heart muscle or the brain⁽²⁾. So, when is it time to go and see your doctor?

• Your fever gets worse. A fever that won't go away might indicate you've got another infection and that might mean you need antibiotics⁽³⁾. Generally, speak to your doctor if your body temperature rises above 38.8°C in spite of medicines⁽⁴⁾ or if you have persistent shaking chills⁽⁵⁾.
• You become short of breath, get chest or belly pain or start turning blue. If you develop shortness of breath or chest pain⁽⁵⁾, or you begin to turn blue⁽⁶⁾, it could be a sign of a more serious problem, such as heart disease, asthma, or pneumonia⁽⁷⁾. Don’t delay calling your doctor or going to the emergency room.
• You can’t keep anything down or become dehydrated. Your body needs fluids to work right. If you can't drink anything without vomiting⁽⁸⁾, you may become dehydrated and need to go to your doctor's office or the hospital to get fluids⁽⁹⁾. Signs that you’re getting dehydrated include urinating less frequently than normal, feeling thirsty, and having trouble keeping fluids down⁽¹⁰⁾.
• You become light-headed, dizzy or even confused. While this may indicate an ear infection⁽¹¹⁾, you can also become dizzy if your blood pressure suddenly drops or if you are dehydrated⁽¹²⁾. If it doesn’t clear quickly after you stand or if it’s accompanied with confusion⁽¹³⁾, seek urgent medical help.
• Your symptoms last longer than a week⁽¹⁴⁾. Or start to improve but then return, but worse than before⁽¹⁵⁾. You develop a cough that produces yellowish-green or blood-stained mucus⁽¹⁶⁾. These are signs that your flu attack is more severe⁽¹⁷⁾. Visit your doctor before your flu turns into an emergency.

References:
(1) https://www.wiv-isp.be/en/topics/influenza/high-risk-groups#who-is-influenza-dangerous-for-
(2) http://ecdc.europa.eu/en/healthtopics/seasonal_influenza/basic_facts/Pages/factsheet_general_public.aspx
(3), (8), (16) http://www.webmd.boots.com/cold-and-flu/flu-guide/flu-emergency-when-to-call-doctor
(4), (6), (17) http://www.emedicinehealth.com/flu_in_adults/page4_em.htm
(5), (14) http://www.nhs.uk/conditions/flu/pages/introduction.aspx
(7) http://www.webmd.com/cold-and-flu/cold-guide/when-see-doctor
(9), (10) http://www.everydayhealth.com/news/flu-self-treat-see-doctor-go-er/
(11) http://www.medtronic.eu/your-health/ear-infections/
(12), (13) http://www.livestrong.com/article/85912-deadly-flu-symptoms/
(15) https://www.thl.fi/documents/189940/257101/THL_influ_A3_juliste2_GBkorj_web.pdf