I have created and tested one of the lower level constructs, using a nested set of std::pair. Basically, this is a tuple with half the fuss. I then created a wrapper around this which used the tuple as the key to an std::map. The entire thing is named SparseGrid on the suggestion of somebody on #gamedev, I forget who. (tell me, will you? you deserve some credit.) I have also written most of the system to load from AC3D and sort into a forest of octees in psudocode and done dry runs.
Drank 7 cups of tea.
Played s.t.a.l.k.e.r. for only 5 hours.
Tomorrow: Fill in the psudocode with real code, and debug.
Anyway, I'd suggest to cycle tea-coffee-99% chocolate on a weekly basis. It seemed to maximize the benefits in my case.
Also consider taking a break. If you're running your hobby, maybe 2 or 3 days off could help you in refreshing.
I'll take a mental note about this. Have fun!