First of all, bay trees require regular watering (but not overwatered) Your plant must have suffered transplant shock. It means the roots were damaged during transplanting. It will recover slowly but just water a little this time. Don't overwater as the roots cannot absorb too much. Else,the plant may simply drown and the roots begin to rot away. Those leaves will just fall off and the tree should produce new branches but probably in the spring. As this is a semi tropical plant - it will grow slowly or not at all in winter.

Next time, before transplanting, water it well. Let the plant drink up as much water as possible. then transfer to a new pot.