I hate those, they're harmless. It's a silverfish. we get a lot of them where I live. I was freaked out the first time I saw one too. You're good though.

A silverfish (Lepisma saccharina) is a small, wingless insect in the order Thysanura. Its common name derives from the animal's silvery light grey and blue color, combined with the fish-like appearance of its movements, while the scientific name (L. saccharina) indicates the silverfish's diet consists of carbohydrates such as sugar or starches.