Transplant shock. You may have waited too long to transplant, and therefore the plant may have become root bound. The roots start chocking themselves and the root ball, relative to the surrounding material in the new pot, is hard for water to penetrate. General gardening and nursery care: transplant once the above-soil vegetation grows to the size of the container. At that point the root ball should also be approximately the size of the container and transplant easily with minimal shock. If the plant grows any larger then the root ball will start girdling itself (go around in circles inside the pot) and you will need to cut the girdling roots and free up the root ball. You can use scissors or a box cutter. On the other hand, if you transplant too early the root ball may not firm up and therefore it will fall apart during transplant and roots will get damaged as the root ball falls apart. If you have damaged roots, a root stimulator may help.