My players have infiltrated the frosty lair of a Mature Adult White Dragon hidden high up in the mountains. By "infiltrate", I mean they had the Rogue infiltrate it, and before he got back, they got bored and decided to kill every living thing in the entire cave complex. Chaotic Evil Arctic Troglodytes and what-not.

Anyway, the final confrontation with the dragon has the Cleric out of healing spells, followed by him getting walloped with a Full Attack directly to the face, dropping him to exactly 0 hit points. The other three players do their stuff, but the Cleric is the one who carries all the healing items, so they're kinda stuck in that regard.

The Cleric uses his one disabled action to cast CLW from a wand to get him back to 13hp (he rolled max). Now that he is no longer disabled, he uses a move action to flee the immediate vicinity of the dragon (who had used his AoO for the round on a different PC). The dragon leaps into the air and Crushes (as in the attack) the Cleric and the nearby Ranger. He rolls near-lowest, dealing exactly 13hp, bringing the Cleric back to 0 and disabled.

The following round, one of the Cleric's magic items kicks in, casting a Freedom of Movement spell on him automatically, getting him out of the Pin, and he casts CLW from the wand again, getting him back up to 10hp this time.

The dragon decides to use his breath weapon rather than continue to pin the Ranger, as he can simultaneously hit the Cleric, Rogue, and Scout all at the same time. The Cleric rolls a 19 on his reflex save (he needed a 19 or 20) and takes exactly 10 damage, dropping him to 0hp.

The next round, the Cleric wands himself back up into the positives again and moves farther away. The Dragon, more than a little annoyed at this point, decided to just Full Attack the Ranger, killing him instantly, and then leaves.

The funny thing is that we've never had anyone dropped to exactly 0hp before, or since. These were all 3 occurrences, bam, bam, bam, all in one session.