oh i've had this!

not only with the forum (i've had days where i can't read the messages and think, well.... i'm just going to not log in at all then, and delete my acount)

but i've had that with books, too

the last book i read was a sherlock holmes novel- and i kept having no interest in reading it (sure, i cared about what happened and how he solved the case) but like you, had no focus to read it

eventually i just skimmed through it and asked someone what happened in the end

it is anoying... i agree- especially when what you're reading is enjoyable