I am glad that this is normal, I didn't want to loose my lionfish. He has a lot of character/personality.
jnsnams, i would not recommend him if you have small fish because they will be his lunch trust me i know i have lost my skunk clowns and my chromises. I thought they would be fast enough but the lionfish is very patient and stealthy. I know one thing also, when you clean the tank or move things around you become very self conscious about the surrounding. Dont want to be stung by one, i have heard it hurts.
Is it also normal to have the lionfish growth to slow down. He grew really fast until he got to be around 6-7 inches long....now it doesnt seem to grow? Kinda curious when he will get to be a foot big.