Worried I have an unruptured aneurysm. I'm overweight and might have moderately raised BP, but otherwise healthy. Vision suddenly dimmed a couple times as if lights dimmed for a second. Also other visual anomalies and localized headache on back head?

I agree this is. something that should be checked out, but an aneurysm is not high on my list. It could be a migraine variant, but dimming vision is not something you should ignore. You should see your Ophthalmologist as soon as possible, or talk with your primary care provider about seeing a Neurologist right away. I do believe imaging, probably MRI with contrast, will likely need to be done. Good wishes:)
Aneurysm . Unlikely to be an aneurysm but see your doctor and get a definitive diagnosis .