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.
Sometimes, however, there is a sudden occurrence of flashing lights with many new floaters or even with a blacking out of part of the field of vision. If this happens, you should see your ophthalmologist right away to find out if you have a retinal tear or retinal detachment.