I agree with Renton - its amazing how things go well at the start, then "normalize".

I played 3k hands of 2nl at 26bb/100 before moving up to 5nl. Despite no difference in the skill level of the other players, I crashed the first 1000 hands there. Now I'm approaching 2k hands and I've only just managed to drag 5nl into positive territory, I think I'm on 4bb/100 but it's heading in the right direction.

Lesson learned = don't focus on session results, focus on playing ABC poker and not making stupid mistakes ... then then BB/hr will take care of itself in the long run.