Lying Face Down
Some interpreters mention that seeing a person lying face down may indicate the loss of their wealth, weakening of their power, and unawareness of how matters are being handled around them. Al-Qayrawani noted that sleeping on the stomach might indicate victory over land, wealth, family, and children. In contrast, lying on one's back might signify dispersion and humiliation, and sleeping on one's side could denote news, illness, or death.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam