It is normal for your BP to rise a little upon standing...same for heart rate (but not excessive).

Those with autonomic issues get dizziness/lightheaded from BP dropping upon standing or heart rate rising. Yours sounds normal.

The incomplete voided (retention) can be from autonomic dysfunction, but may also be from some other cause. You might want to see a urologist.

Constant dizziness (even while sitting) does not sound like autonomic neuropathy without some sort of significant change in your BP or heart rate or change when you stand. It may be Vertigo, which can be from an inner ear problem. I'd start with a visit to your primary care doctor...who may refer you to an ENT.

The most common autonomic problems are: increased heart rate upon standing (POTS), drops in heart rate (bradycardia), increases in heart rate (IST--inappropriate sinus tachycardia), drop in BP upon standing, difficulty initiating urination or complete emptying (retention), delayed gastric motility/emptying, temperature regulation, vasospasms, livedo reticularis, sexual dysfunction, etc.

Although autonomic neuropathy can be associated with diabetes, you don't seem to have the most significant aspects of this (good news). You should follow up with your general doctor about the dizziness and urine retention.