It is normal , they are stressed , when adding a new fish it is best to leave the lights out for the day (when we add them it is in the evening just before lights out . I am able to get them in and add the water that I used in drip acclimation with only a minute or 2 to spare then the lights are out ) They need to feel safe in thier new surroundings and will hide till they are sure some big boogie man isnt gonna make them snack . Give them a day or 2 they should be fine .
BTW what kind of fish did you add , how many and what size tank , and are their any other inhibatants in the tank already?