Could you post your water parameters (temp, pH, ammonia, nitrite, nitrate)? That would be the first thing I'd check if a fish was behaving abnormally. Also, did you notice any violence between the two gouramis? Usually honey gouramis are more mild-mannered than other gouramis, but there's still the possibility that the more active one beat the other one up and has him hiding in a corner.
Not to rain on your parade, but you're eventually going to need a much, much larger tank for those bala sharks, as they eventually get to 16" in length.