Holistically, speaking, maybe it's all related

Insulin defects may figure in mental illness - Health & Science - International Herald Tribune

Insulin issues, such as those seen in diabetes, are especially being studied in older adults, where cognition impairment appears to differ based on insulin's and blood sugar levels' stability. The same metabolic syndrome that puts people at risk for obesity, diabetes, lipid issues, and heart and vascular disease may also increase the chances of Alzheimer's, for example. Also, there may be an insulin component to differences found in schizophrenic brains. Anti-psychotic drugs seem to help protect schizophrenics and those with bipolar disorder from developing diabetes.

In my case, it looks like metabolic syndrome --> obesity --> sleep apnea and diabetes --> depression, anxiety, and cognitive issues. So...now I'm being treated at all levels of that chain, so hopefully it should help. My depression, sleep apnea, and anxiety issues are all under control. I'm being treated for cognitive issues including ADHD and those related to obsessive-compulsive disorder. Maybe the insulin resistance is the last brick I need to feel better and wholly myself again.