When a character has less than 0 but more than -10 HP, they are considred "dying". According to the SRD:
A dying character loses 1 hit point every round. This continues until the character dies or becomes stable.
However, a character or creature with damage reduction takes an x-amount less from any source of physical damage, which arguably includes the above. Obviously (to me), having damage reduction doesn't automatically mean you're immune to bleeding out. However, is there any official source that explains this? If so, what does that source have to say about the matter?