It is possible to have mild astigmatism and not know about it. This is especially true for children, who are not aware of their vision being other than normal.
If you suffer from headaches, eyestrain or blurred vision, there is possibility that you have astigmatism. Most people with nearsightedness tend to have astigmatism at the same time.
Some people may have mild astigmatism without any symptoms. It's important to have comprehensive dilated eye exams to make sure you are seeing your best.