Writing two things at once is a tricky, yet energizing thing.
Right now I'm working on an adult novel, very serious and leaning into the magical realism, and a YA novel, leaning toward the alternate future/adventure, kind of story. Two very different things.
But I'm having fun and writing the two together is pretty entertaining and kind of schizophrenic. When one starts draining me, I switch to the other. My brain twists and turns to catch up. I'm writing two pages a day--one for one book and one for the other. And it's fun. I highly recommend the trying of it for those of you who have been plugging away on just one thing for a while.
Eventually, one of these will demand more of time--especially when revision comes up--but for now I'm just cutting loose and that feels good.