Funny Mark, I'm in the same low energy spot. Vicki and I had a rush of activity for several weeks and I was working day and night on "Nightcallers" and then I just hit a wall and been floundering. I blame it on Summer, the heat, the natural ebb and flow of work energy, etc. I feel like it's just starting to pass but I'm also not in a hurry to start the race again. I'm just giving it time.
Very sorry to hear about your brother, also. That kind of thing is its own energy-sucker and would have an effect even without the letdown of your project ending.
I also have a theory about the election season and the twists and turns political discourse seem to have taken just lately. I think people are taking a breath because no one is sure who they're supposed to be mad at anymore, but that's just how it seems from inside the NY bubble. But there's definitely a sense of inertia permeating everything.
Roll with it, it'll pass and you'll be having fun one day soon and thinking, "oh yeah, THIS is what it used to feel like!"