I've always (at least since my teens) had periods of time where I'm much more productive and I am seemingly able to think much more clearly and comprehend things much more easily. Similarly, I have periods where I'm much more forgetful, distracted, and dull. To me these periods have always been strongly correlated with hypomania and depression. I haven't noticed any permanent cognitive decline yet and I'm hoping that won't happen. I have noticed that some of the negative symptoms linger between episodes but I think that can be contributed to the fatigue of trying to recover from months of depression. Some of the meds can definitely make me a bit loopy as well.