Maybe not fatal, but I'd hazard it could affect your breathing a lot if you're hanging like that and the whole weight of the body (or most of it) is on those reddened, blooded breasts. To say the least it might be a long time before the sub recovered.

"His flesh felt tough on my teeth, says Armin, still incensed at the fact that Bernd- Jurgen tricked him about his real age" (from a newspaper article a week after German cannibal Armin Meiwes had been arrested). The guy had explicitly put an ad for "men up to 30 who wish to get eaten" but Bernd-Jurgen B. who responded was in fact around forty.. :-)