They do look a tad droopy... Lots of potential reasons for this. Off the top of my head, could be:

-Your humidity is low so they are holding on to their water and getting weighed down.
-Something in the water if it is tap (excess minerals/salts).
-They are getting too much water/not enough oxygen. (I don't do drip, so I don't know how that is regulated.)
-18/6 might be just a bit too much for them to handle at this stage, and going down to 15 or 16 for just a week or so might de-stress them.

What kind of lights?

If you don't have a fan blowing on them, get one going ASAP... This will strenghten the stems, and might even perk the leaves up a bit.

Hopefully a Drip Master will stop by here and give ya the wisdom I lack. *grin*