Welcome to AA.
Did you see the happy one bothering or chasing the hiding one?
How long has the tank been up and running?
Do you have a test kit and if so what are the readings for Ammonia, Nitrite and Nitrate?
How often and how much water do you change? Do you use dechlorinator?
What are the other tankmates?
How long have you had the DG's? And the rest of the fish?