People look for symptoms when something feels wrong, such as tiredness, headaches or a cough. Those are not signs of radon in a home, and no health effects other than lung cancer have been established. A household that feels fine is not evidence that the level is low either.
What radon does is raise the risk of lung cancer over time. The radioactive particles it produces can lodge in the airways when breathed in and damage the cells there. Not everyone exposed to elevated radon develops lung cancer, the time between exposure and disease may be many years, and the risk is much higher for people who smoke.
If you have symptoms that worry you, see a doctor about them, and mention any radon result you have. That conversation is about your health; the test is about your house, and the two answer different questions.
What to do next: test the lowest lived-in level of your home. A that runs at least 48 hours with the house closed up gives a first answer, and the interpreter explains what the number means.