Being of Two Minds — Pamela F. Service

Connie Hendricks was a typical American teen except for her dizzy spells, when she would pass out. When this happened, she entered the mind and soul of Prince Rudolph, the fourteen-year-old heir apparent of Thulgaria, a small European country. Prince Rudolph had spells too, when he entered Connie's mind and life. Everything was just fine, and their "trick" was their special secret -- until Rudolph was kidnapped while Connie was inside his mind . . .From the Paperback edition.