The dizziness while driving, especially on the highway, is almost certainly due to neck muscle and upper back muscle "trigger points". These "knots" can be massaged away and stretching helps keep them from coming back.
This is called trigger point massage, or myofascial massage. Check out the book "Trigger point therapy workbook 3rd edition" by Clair Davies. It is the STERNOCLEIDOMASTOID (SCM) trigger points that create the dizziness while driving.
You may also have trigger points along the upper back and between the tops of the shoulder blades (upper trapezius). These trigger points will create a dull ache at the base and back of the neck and create an unsteady feeling while just standing or walking around. Some people call this feeling "brain fog". It can be eliminated by trigger point massage along the top and in between the top of the shoulder blades. The best stretch to get rid of the brain fog is to bring the tops of the shoulder blades together and arch the neck and head backwards like to look at the ceiling.
The dizzy driving SCM trigger points may take a few days or weeks to get rid of all of the trigger points if you have a lot of them. You have to check all along the whole length of both the front one and the back one, and also down under the collar bone where they attach to the breast bone. The SCM trigger points in the neck can cause pains in the forehead, jaw, behind the eyes, the top of the head, near the base of the throat where they attach to the breast bone, and the back of the skull down at the base. Usually you will notice no pain in the SCM neck muscles themselves until you squeeze them to find out where the trigger point are. All kinds of neck stretches help keep the trigger points from coming back as strong.
This all probably sounds like new age kook stuff, but trigger points are real. I had the dizzy while driving problem for 13 years and no doctors knew what was causing it or how to fix it. This included a regular massage therapist, two chiropractors, ENT specialist, neurologist, and the Yale Balance Center.
Make sure you do not have poor upper body posture like thrusting the head and jaw forward while staring at a computer screen for hours at a time.
Hope you see this and good luck.
P.S. The driving down the hill dizziness could also be related to the "brain fog", which is the upper and middle back muscles. The stretch where you pull the shoulder blades together and tilt your head and neck way back helps this condition immediately. If you feel upper back and shoulders getting tight or hunched any time while driving, try to relax the shoulders and when the road is clear try the stretching and massage the area over the top of the shoulder blades.
I suspect you did not get a thorough eye exam. Certain people develop "night nearsightedness", generally starting over age fifty. At night the eye behaves differently. These individuals may require special prescription eyeglasses nwhen driving at night.
Another possibility is cranial nerve palsy secondary to diabetes. This means the eyes may not focus properly, creating a loss of balance. In the daytime there are sufficient visual clues to overcome this. At night those clues disappear.
Get a consult with an opthamalogical neurologist.