I'd disagree with iburmaster's answer. People who talk about near-death experiences are most often talking about what goes on their mind when their body is very close to actual dying (as in changes in vital signs and other things that go on when, say, someone is close enough to death that their consciousness is changed (or even when they've "technically died" but been revived).
I was in a car accident in which the driver, inches away from me, was killed. I saw the other car coming and had a brief moment to truly believe I was going to be killed and even think about my parents (who were alive at the time). Medically (and fortunately), I didn't come anywhere near death. I was in and out of consciousness for a day or so, but even then I wasn't near death. I just had a "good" concussion. To me, that was NO near-death experience. That was just "A Close-y". :) (A close call) It had its own kind of impact on me, but there was never a time when I was close to death ("near" death). A lot of people told me I was lucky to be alive (and I knew I was), but I didn't "almost die".