what are the water readings for Ammonia, Nitrite and Nitrate? sounds like he is irritated by something and water chemistry is the number one cause for those symptoms.
Yes, it's normal behavior if there is something wrong. He's trying to scratch something off himself. Can you see anything on the fish like cuts, marks, spots? Fish flash when they are trying to scratch something off like a parasite ( ich, etc) or after an injury or if something is amiss with their water. What are your parameters and what water conditioner have you been using? Tankmates and are any new?