Good thing your Koris slept for 4 weeks. This is necessary to cleanse the body of toxins. Otherwise, he would have started eating and would have died in 3-4 days. Usually, if the fish was caught with cyanide, or if it was kept in a very concentrated copper solution for a long time (on a fish farm), or if it was poisoned with ammonia during transportation, etc. The fish needs time to clear out the toxins. Those Wrasses who dug in and did not eat anything will survive, those who started to eat will immediately die with a probability of 80% approximately.
Soon he will begin to forage during the daytime and stop hiding during the day.
To speed up adaptation, feed him before turning on the light for a couple of days. Wake up early in the morning.