I just had an epiphany while doing the light tube and I want to take the time right now to jot it down in case I forget.
Lately I've been noticing a lot about the way my lazy eye feels when it moves and tracks things. It feels good. But when I'm not tracking things or moving the lazy eye, I let it disengage--meanwhile the fixing eye never disengages. The fixing eye is never not looking at something, although that's not true of the lazy eye. It's often not looking at anything at all, provided that it's looking in roughly the right direction to avoid diplopia. What I mean by 'disengaging' the lazy eye is analogous to locking your knees while standing. It uses less energy and you might have decent posture, but you're also less ready for action.
So while doing the light tube, I've been focusing a lot on getting the scene as bright as possible--but now it's occurred to me that while doing that, I should not--or ever, really--disengage the lazy eye. That's probably what my whole freaking problem is. When I disallow it to disengage, it's quite a workout, but that's not really a problem. I'm sure that when I get used to not disengaging it, the fatigue will go away.
It seems really obvious--it's just a connection that I had failed to make before. The fact that it's disengaged is probably what's causing the 'driftage' that I've talked about. Damnit!
It's just the same theme recurring again and again. As I progress and gain experience with exercises, I become more and more aware of what I'm doing that's wrong, what I should be doing, and what my next steps should be. The next step is conscious non-disengagement of the lazy eye.