If a chronic source of infection such as sinus, gradually became worse and germs entered blood, how long could you potentially be feeling ill?

Depends on treatment: When germs enter the blood stream to make you sick, it is called septicemia, a potentially serious condition. The diagnosis is by blood culture and it requires hospital admission for IV antibiotics and close monitoring until cultures become negative. Treatment for such a condition is 10-14 days, not all of which needs to be in hospital. Feel better:)