I'm not so certain that the issue is the definition of the term normal, so much as it is the value (positive or negative) or association (healthy vs. unhealthy) the term implies in a medical or social context.
One of the most common reasons for blurry vision while wearing contacts is that your eyes are dry. Some people have a medical condition that causes dry eyes, called dry eye syndrome, but others' eyes are irritated by the contacts themselves.
That's why when you have allergies your eyes can get watery or itchy, and when you're sick it can feel like your eyes are heavy. Anxiety - a common condition affecting nearly 20% of Americans and millions more around the world - also has its own vision symptoms.