I have similar problems. Now that I am seeming (and feeling) more and more normal I am getting a different set of challenges, in that others (and to an extent myself) are starting to treat me as if I am fully recovered, when I actually still need to be careful.

Something that seems to be helping is that I sit down with my supervisor every two weeks and plan what hours and tasks I will be aiming to do over the next fortnight, with a very gradual increase over time. Then if I'm not up to something I can just say "sorry, it's not in my return to work plan, but I do hope to be able to help with that stuff soon" rather than having to take the responsibility myself and justify it in terms of symptoms etc.

Good luck! The fact that you are having this problem at all is I guess a sign of recovery, which is good - though when all you have to show for recovery is that you spend more time at work and are left equally knackered in the evenings it all feels a bit hollow for a while!