Usually, regular Dom/sub dynamics between Kylo and Hux is enough for Hux to get what he needs: have control taken from him, get praised for doing a good job, just let go for a bit. But some times, it just isn't enough.

In those times, what Hux needs is for Kylo to "switch him off". With the Force, just take away his memories, his need for control and his reticence at gestures of affection. Just make him a sweet little pet who enjoys doing what he's told, has no memory outside of the room he is in and his master. He just wants to be eager and be praised for it without the associated shame.

It's all temporary of course. They decide before hand for how long it's going to last, and Kylo pulls him out of it once they reach that time.

Please, no Kylo taking advantage of this and humiliating him!

Bonus:
+ From the POV of "switched off" Hux, who is just so eager to please and loves his master so much.
++ It's not all sexual; the play can also come in Kylo feeding Hux, pampering him, giving him simple tasks just so that he can be praised for doing them well.
+++ After a particularly hard day, when Kylo pulls him out, Hux doesn't feel like he's had enough. He asks Kylo to put him back under.