Daniel's friend had surgery last week. One second the doctor was counting down. The next second he was waking up. Hours had passed. He remembered none of it.

Daniel wants to know what actually happened in between.

The answer starts with a correction most people need. General anesthesia is not ordinary sleep. Sleep is a natural, reversible brain state. Anesthesia is a drug-controlled state designed to make you unconscious, unaware of the operation, and unable to remember it afterward. For most people, the experience feels like an instant jump from before the surgery to after it. No time. No memory connecting the two moments.

Researchers think some people may still have dream-like internal experiences during anesthesia -- but usually none of it becomes part of the story they remember afterward. The gap is a memory gap, not necessa ...