I have occipital headaches which are not diabetes related, rather I have spondylosis and mild stenosis in my neck. The spondylosis was diagnosed around 35 years ago and the cervical stenosis after an MRI scan around 9 years ago certainly years before I was diagnosed with diabetes. When the spondylosis/stenosis is irritated, I experience most of the symptoms you describe. Nausea, loss of balance, numbness, tingling in fingers, memory issues. I was told to avoid lifting heavy objects as that irritates things and I experience pains across my chest. I am also limited in doing many of the activities other people take for granted as if I look up or down for too long I lose concentration and start to feel nauseous which can take a few days to resolve. Most recently I have been having headaches which start at the base of my neck and work their way around the back of my head. I also experience icepick headaches but not sure these are related to my neck issues I was recently re-referred to a musculoskeletal consultant as I was having major balance issues, when I mentioned the headaches, he confirmed these were occipital headaches. My consultant sent me for an MRI scan and I am still waiting to discuss the findings of that, however he also referred me to physio.
Physio gave me very simple exercises to do which have helped a great deal, for the most part my balance issues are now resolved and whilst I still do have some issues, I am not stumbling around the way I was neither do I get nearly so many headaches. I am not saying that what I have is the same as you are experiencing but there do seem to be similarities. I am not a gamer, but I did work in the computer industry for many years and part of my problem was constantly looking at computer screens.