I'm assuming this is a clone. If so, it's pretty common for some clones to droop temporarily, but most will usually regain turgidity after a week or so. I keep clones in a humidity dome until a good root system has been established before planting into a medium. Also, cutting away half of the fan leaves from clones will help to reduce transpiration, and increase surface area available for light. Since clones don't immediately have a root system, it's much more difficult for water uptake through the main stem to take place. High humidity is actually a good method for reducing transpiration.