Hi willthiswork,
Yes, unfortunately we're not imagining it. It's well documented that there's a certain amount of cognitive impairment in early recovery. IIRC, the rate of axon formation is slowed at first but in most cases the brain starts to repair itself after 6 months or so if abstinence is maintained. There's plenty of research on this if you google it.
This aspect of recovery is a particular frustration for me as my work depends on abstract reasoning. It seems the 'brain fog' is just another penalty we have to pay.