Everything here runs under consent and the ability to pause or stop — either of you, at any time, and staying down is never an obligation. The three structural rules: the giving partner's weight stays on their own supports, the receiving partner's breathing stays free, and the way up stays clear — a rehearsed signal, no weight pinning anyone.
Some situations deserve a second look before going prone, and the research here is thin enough that someone who knows your situation beats a generic list: pregnancy (belly-down plus a partner's weight is a bad combination), chronic back or hip pain, breathing limitations, larger bodies where prone concentrates load, and trauma histories or claustrophobia — face-down, covered, and unseen is precisely the setup some nervous systems read as danger. If prone doesn't fit, side-lying and supported variants carry the same dials with less structural disadvantage. And if pain with sex is persistent or getting worse, that's a clinician question, not a positioning one.
One more thing worth saying plainly: if discomfort you've flagged keeps getting ignored, that's a consent and relationship concern, not a positioning one.