When it comes to describing someone lying with their face down, there are several synonyms that you can use. One of the most common expressions is "prone," which means lying flat with the face downward. Other synonyms include "face-planted," "prostrated," "lying flat," "facedown" and "supine." Another phrase you could use is "lying with their face buried in something," which implies that the person is resting their head or face on a particular object. Whether you're writing fiction or non-fiction, using these synonyms for the phrase "face down" can help add variety and depth to your descriptions, making your writing more engaging and captivating for readers.