In my case I think the fuzz-brain's from needing extra sleep and not getting it (I do get 8 hours, more or less). But I've always been that way - unfortunately I didn't figure it out until long *after* my college years, in which getting 4-6 hours of sleep a night probably had a lot to do with my grades. Looks to me like needing more sleep from more exercise is common but maybe getting stupider from it is less so. ANd with that said I will get off LJ and onto the erg. For the next three hours. :-(