[lph]

I've experienced what you describe with Anki also. Moreover, I've felt there needs to be a model of the user's current acuity, because it's highly variable. If I make one error, then yeah, apply the SRS algorithm to that card. But if I get 50% more errors than expected, maybe I'm just exhausted and the session should take that into account. I used to use Anki to study Chinese characters on the way home from work, and after a long hard day with poor sleep the night before, I hit the learning wall a lot faster than usual.

tl;dr a bonus effect of regular Anki practice is you can detect when you're in a stupor