You know you're addicted to Zelda ..
When you see your shadow and brace yourself for a duel with it.
When you're out of Visine, so you bring a frog to the pharmacy and ask them to use it to make eyedrops.
When you see a horse and Epona's song immediately starts playing in your head (this one...
You know you're addicted when you're at someone's house and break their pottery assuming that you can just exit the house and re enter and it will all be as good as new.