I'm a stickler for semantics and would argue against this practice as it has been described. Instead of creating a context I suggest creating a reference list instead of an action list for dummy things like refilling your stapler, watering your plants and cleaning your toilet.
The key difference between a reference list and an action list is that reference lists don't contain items that are permanently crossed off. I have such a list that includes things like "empty dishwasher", "fill dishwasher", "empty dish drainer", "water plants", "dust furniture", "vacuum floor", "defrag hard disk", etc. I don't cross off these things when I do them.
I assert that "Brain Dead" is NOT a context. It's a level of energy (the 3rd of 4 factors that limit your choices of what to do in the moment). Contexts are the first limiting factor of your choices. They are aligned to key locations or tools that are required for you to take action. If you treat @BrainDead as a context you'd be faced with a mix of things that you can and can't do at the moment. You'd have @Braindead things that you can only do at home and @BrainDead things you could only do in the office. Mixing those things together is BAD!
I've practiced GTD for six years, read the books and seen the mastering workflow seminar. Nowhere does DA mention tracking energy level or time required on action lists. Doing so creates unnecessary overhead to the system. That's what your intuition is for. The system is there to do the remembering part for you so that your brain can intuitively think about the work instead of trying to think of (remember) it.
You will have defined work on your action lists that you could do when you are brain dead, too. As you review an action list to decide what to do next use intuition to decide in the moment if you have the energy to tackle an action.
At the end of the day do what works for you. I'm just cautioning you about the dangers of mixing semantics and creating complication and resistance to the system.