Let your doc know right away. This sounds like it might be a complication of the cold. You might have labyrinthitus, which is an infection of the inner ear which can be caused by a virus of bacteria - I woke up one morning and the room was spinning. I was off balance, too, and if I tried to concentrate, like working on the computer, would get nausea.
My doc treated me with a round of Zithromax. He also prescribed anti-vertigo medication which caused me to feel very sleepy. Symptoms were much better in a week, but it took months for some minor symptoms to go away (if I suddenly bent down, would get dizzy). At least the vertigo went away within a week. He said the vertigo, which could attack at any time while the infection is active, is especially dangerous if you are driving a car, because you could have an attack of vertigo and get in a traffic accident.