Apple Wireless Keyboard not connecting automatically on wake
Resetting the SMC should be able to fix the issue. Note that this will reboot the MacBook, so you will lose any unsaved work.


Shut down the computer.
Plug in the MagSafe power adapter to a power source, connecting it to
the Mac if its not already connected.
On the built-in keyboard, press the (left side) Shift-Control-Option
keys and the power button at the same time.
Release all the keys and the power button at the same time.
Press the power button to turn on the computer.


Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.