Moving from the Abode of Islam to the Abode of Shirk
Scholars have said that if someone sees themselves moving from the abode of Islam to the abode of polytheism (shirk) in a dream, it may indicate that they disbelieve in God after having believed, which is considered a fundamental shift in faith.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam