Dr. Who and Regeneration of each Doctor?

Okay so I'm confused. I'm behind on Dr. Who and finally saw the episode where the 10th doctor regenerates into the 11th (and current) Dr. I had the understanding that when each incarnation of the doctor was at death, he regenerated into a new form... it was still the same man, same memories, same feelings, just different looks with new personality quirks. Time Lords are basically immortal, though they limit themselves to 13 lives, (but since the Dr. is the last time lord, it is questionable if this rule they made applies to him... I doubt it will since we're already on Doctor 11) Anyhoo... when the 10th doctor regenerates into the latest doctor... He talks as if he's going to die, like he's going to be gone, his consciousness will be no more, his memories will cease to exist and a new person is going to take his place and live his life,... etc. But I always thought - It is the same person, just different looks, different personality quirks, but basically, the same guy who saves himself from death by regenerating his body just before he dies. Did I miss something? I haven't seen the whole series from start to finish. I watched re-runs of the Tom Baker years through my brothers VHS tapes, and the new series since it re-started with Christopher Eccleston (the 9th doctor) So maybe I don't quite get how the doctor works. Does he regenerate before death to keep from dying... or does he die and becomes a new person as if starting from scratch?