Could be an inner ear infection.
I had the same thing long before my AN in 1983. Woke up one day and the room was spinning. It stayed like that for over a week, gradually easing up. I went to a doctor who told me it was "viral vestibulitis" (inner ear infection) and gave me a
hit of Antivert, more commonly known as "Meclazine". I can't remember if it worked. What I do remember is that the night before my affliction I had gone out to see a loud band at a local club. The loud noise could have set it off. I also recall a strange visual effect I had been experiencing for several weeks before the vertigo. When I'd wake-up, my vision would roll very slowly, from bottom to top, like an out-of-phase horizontal control on an old T.V.. As I went about my day, the rolling would gradually go away. So I knew something wasn't right. But I think it was the loud music that really set it off.
It is interesting that during the period I was getting sick from the AN, I was a working musician, playing 4, 5, and even 6 nights a week, driving all over, virtually deaf in one ear, lightheaded, plagued with double vision, crippling fatigue and malaise. I couldn't call in sick; neither did I have any health insurance. I kept pushing myself until I literally couldn't put one foot in front of the other and I was in pretty good shape at the time, jogging 5 miles a day on trails through the woods.
I had been pulled over marked lanes and suspicion of DWI four times. One time, and for the first time ever, I actually fell asleep behind the wheel ....and survived by the grace of God. I snapped to broadsiding a snow bank against the guardrail on the opposite side of the road. Luckily, no one was coming the other way.
Inner ear infections are not to be taken lightly; I know a girl who lost her hearing in one ear from an inner ear infection.