Since you have other symptoms in the same autonomic class (the urination and dizziness upon standing), you should consider a tilt table as well, for possible orthostatic hypotension or POTS.

Just a hint: In the morning, try sitting up in bed first (don't get up) and stay there for a few minutes. THEN, stand and see if it helps your BP to adjust to the position change a little better and reduce (might not eliminate it though) the lightheadedness upon standing.

You can check your own BP while you are laying in bed, and then check it standing. If your BP drops more then 20 mm hg systolic (first number), then try it again the next morning after using the hint and see if your numbers (and symptoms) improve. Also see if your heart rate is increasing significantly when you stand.