I was driving to pick my daughter up from work. I had my bright lights on to see any deer ahead in the road. I was in darkness for the mile stretch that I saw the object. I saw a dim glow out my side window and that it was a patch of fog traveling with my vehicle. I estimate it was about 10 ft off the ground and about the size of my vehicle. I began to attempt to debunk it, thinking it was a reflection of the interior of the car - no. I thought the headlights were causing a reflection on area fog. No. It was too far back to be my headlights and there wasn't any fog in the area. I was on this road for exactly one mile traveling south around 40mph. I kept looking and looking at it every few seconds. I got to the corner and turned right. It was gone. Nothing had changed, it was still dark and my headlights were still on bright. I kept checking out the window for most of the rest of the way to my destination but never saw it again. On the way home I took the exact same road but now traveling north. I didn't see anything and neither did my daughter, who was by then with me. I don't know if this was a UFO or something else entirely. I was unable to debunk it while it was occurring. While it was happening I felt disbelief and curiosity. No real fear. Now as I sit here typing this I am shaking a little. I might have trouble sleeping. Is a delayed fear reaction normal? I should have panicked while it was happening but didn't. It was so close to me too.