You provided one clue to the likely answer to your question when you said, "I woke up this morning to find a couple leaves of one of my FLFs pointing straight up", and a second clue when you said, "I haven't watered it in a couple days (I'm waiting for the soil to dry out)". There are only a couple of things that ultimately affect the leaf's attitude (the spatial position it occupies). One is turgidity, which is essentially internal water pressure, and the other is phototropism, or the plant's reaction to light. We can eliminate phototropism because it wouldn't occur to the extent you could notice it over the course of a day, unless you were specifically conducting an experiment to measure it.

Here's what I think. Your plant was somewhat wilted because of an excessive amount of water in the soil (too much water deprives the roots of oxygen, which limits their ability to function efficiently/normally). This caused the leaves to change their attitude (hang down a little/wilt). During the dark phase, the openings in leaves (stomata) that allow water to escape from the plant are closed (or very nearly so). This means that a root system that wasn't able to keep up with transpirational water loss during the day while stomata are open, WAS able to keep up with water loss at night while those openings were closed. Couple this natural rhythm of the plant with the fact you were waiting for the soil to dry down, which means that root function was probably regaining efficiency with each passing day, and you can see how the pieces of the puzzle fit together. The plant simply regained its normal turgid state and the leaves went back to their pre-wilt positions.

FWIW, if FLF and rubber trees (F elastica) wilt badly, the leaves are very often permanently affected and unable to recover their previous attitude.

Al