I had the exact same problem! My MacBook Air was sitting overnight and unresponsive to keyboard & trackpad in the morning. Had to reboot using the power key, which was still working. Based on above comments, I hooked up an external keyboard and mouse, which worked! I turned Bluetooth off and on again, and that restored my internal keyboard and trackpad functionality. I tried it because of the above comment on the MacBook Air thinking a Bluetooth mouse I had for my desktop was around. Worked for me with minimal effort.
