It happens! It's happened to me a lot over the last few years, on and off, for various reasons. Lately it's hit me harder than I've ever felt before. I might actually need a real, genuine D&D break. I don't think it's a total gaming burnout, though....thank goodness....as I still feel keen to continue my ongoing Call of Cthulhu and periodic Starfinder games, but in many regards my interest in D&D style fantasy is cripplingly low. It doesn't help that real life has dramatically lowered my free time to prepare and plan for games; without that time (or interest) I can only sustain a game for so long before I feel like the law of diminishing returns has kicked in. For reasons I haven't fully identified, that has most definitely happened to me with D&D right now.
I could speculate (and have) but the truth is, it might just be a genre thing. For those of you thinking this sounds crazy, keep in mind I've been more or less running (as GM exclusively) two weekly games for almost 11 years straight now, and prior to that still on averaged managed 1-2 games per week prior to that, going back to like 1989. That's a lot of gaming.
Most of the gaming has been absorbed by D&D and its relatives, so it stands to reason that it might be the genre I have most deeply drunk of. I am pretty sure (but not 100% sure) it's the genre and not the system. One way to test this would be to break out of D&D 5E and try some other fantasy games. I recently ran two sessions of Mythras to hold Saturday over while I found time to prep the next Call of Cthulhu arc. It was fun, but then Mythras didn't have prep time, either, so it became less fun as a result. The problem is, even when I have the prep time, I'm having trouble finding the interest....fantasy is really, really REALLY played out for me, I think. Not much genre wise left for me to explore or be surprised by.
One thought is: let someone else run games on Wednesday for a while, see if that rekindles my interest. Truth is, I'm so "jaded" from being a GM for decades that being a player is hard and ultimately disinteresting...but taking a break has inevitably helped me to recharge the old GM engine, so maybe that would work out, anyway.
Anyway, I'll work out some sort of plan, maybe tonight as I wrap the D&D game. I know I'm not completely burned out as a GM, because I have lots of interesting ideas I want to explore in other genres, using Starfinder, Traveller, Savage Worlds, White Star, Call of Cthulhu and even Cryptworld. My plan is to convince the group to try one of these. When I'm ready, maybe I'll dive back in to fantasy with something a bit nonstandard, such as Fantasy AGE or Symbaroum.