I had memory problems and concentration. Of course I am older, so I was joking that it's just early senility, lol!

But the lack of concentration, being way too easily distracted, all that seems to be because I did not have, so to speak, my mind dully engaged. It was like my mind had gone elsewhere (hidden in a closet getting drunk on it's own sorrow) to pay attention to such things piddle things as staying on a task or digging for a memory.
Replaying bad memories, on the other hand, seems to fit with the closet of sorrow thing. I see depression as a mind stuck in telling itself "nothing is worth anything, i am worthless," etc.. Bad memories that reinforce this notion would be just what it wants, and the bugger can't let go of them.

Then again there are bio-chemical changes associated with depression that may explain it a bit differently.