The speed your refering to is just the connection rate. Think of it as the speed limit on the road. It doesn't tell you how fast your going, just the fasted hypothetical speeds on the connection. Usually the real world speeds are alot lower then hypothetical speeds. Usually a wireless network will decrease the rate when the signal level decreases, so thats probably happened.
Why that happened, I am unsure. What kind of router do you have? And what kind of laptop? Tell me a little bit about your network?
