Don't make a no-energy context
I think making a @no-energy context is the wrong way to go about it.
Not every mood is consistent. One afternoon I might feel sluggish but be willing to read some magazine articles in my To Consume stack. The next afternoon I might also be sluggish, but find reading requires too much concentration and clean the kitchen, instead.
I find my Next Action list freeing because I can scan it and do pretty much whatever I feel like doing from the list. (Caveat: I divide deadline-based projects into chunks and schedule them on Daily Action cards.) I'd suggest just trusting your feelings at the time and choosing from there. (There are also the options to go through your To Consume items or to just do nothing!)
My guess is that you're not fully capturing enough. Does your next action list have "change lightbulb" and "re-thread yoga pants" on it? Do you have "Brainstorm ideas for X Project" listed? I always have *something* on my list I can knock off no matter how low my energy level.
attack/prevent the low-energy
I think you can go through your context lists and see if anything fits your ability at the moment or review your calendar to see what has a horrible deadline that will make you find your energy but I think the real problem is to find ways to counter or better yet, prevent, low energy, or go with the flow and rest when you need to (as long this is not a "professional" avoidance tactic).
Just some ideas: track the energy level (degree, physical or mental, when, where, possible reason).
Look for causes, search out possiblities whether they be common, idiosyncratic, good reasons, silly reasons, poor nutrition, engaging with people that use up your energy, too many open loops (that's me), certain work days are in a noisy and annoying environment, etc.
Look for antidotes that you can apply or prevention tactics.
Find uncommon solutions. A yoga teacher I knw proposed that if more people watched TV in various yoga postures they would gradually want to move about more and gradually disconnect from TV.