What Causes Giddiness, Unsteadiness, Nausea With Vomiting?

I feel giddy sometimes and get unsteadiness in my movements.Then I have to lie down on bed but a slight movement brings the giddiness. Sometimes I feel nausea in travel and if the road is bumpy and the journey long, I vomit.My doctor says that it is due to Spondilosys and has suggested certain exercises.