I've been in those slumps too. For me, it's about breaking it down to the basics. I focus on the process, not the outcome. Instead of thinking about the end goal, I focus on putting one foot in front of the other. It's not about being excited, it's about showing up and doing the work. And sometimes, that's enough to get me out of the slump.
I'm a fan of the 5-zone system too. For me, zone 2 is for recovery runs, zone 3 for endurance, and zones 4-5 for harder efforts. It's not one-size-fits-all, but it's a good starting point. Experiment and adjust based on how your body responds.