Single-Player Lag.

While continuously flying or sprinting in single-player mode, the game, after a short time, seems to stop in all-aspects. Mobs no longer perform any actions (even noise), chunks stop loading, light-levels stay the same in some areas, blocks don't drop items when broken, and blocks can't be placed. This usually occurs less with sprinting and more with flying.This can also last as short as 2-5 minutes or as long as 10 minutes. This only happens within a single-player world. This doesn't appear to be a normal time-span for chunks to catch-up on loading to me. It has never occured to this extreme measure in the past (except in multiplayer with a bad connection).