Yes you can have Lupus for awhile and not even know about it.
Lupus can show other symptoms that may be similar to other illnesses that would not alert you to having Lupus.
The only real way to know for sure if you have Lupus is to get tested by a doctor.
Lupus can mimic other conditions such as fibromyalgia, rheumatoid arthritis, and various others that affect the same organ systems.
If Lupus goes untreated it may sometimes lead to life threatening infections.
However in most Lupus Patients the Lupus if left untreated leaves to Fatigue, Joint Pain and Rash which is non life threatening.
It's a good idea to have the Lupus Treated just to prevent further infections and conditions that can arise from it.
Most people with Lupus live a normal lifespan and there's really no life expectancy of someone who has Lupus.
Just because someone has Lupus does not mean that you will not live a normal life expectancy.
There have been many people with Lupus who have been living with Lupus for 40 years and sometimes longer.
But your overall health can also factor into the lifespan of a person with Lupus and if you're say in your 70s then you might live another 5 or 10 years with the Lupus.
But if you're in your 30's when you have Lupus then you may live another 40 to 50 years before you die.
Lupus does not always cause a person to die any sooner than those without.
However if left untreated the Lupus may progress and cause other deadly infections.
So if you do have Lupus you should get treatment for it increase your chances of living a normal lifespan.