by 
Honestly, I was just thinking of the stability of OSX Yosemite and just after suddenly the connection with Bluetooth mouse is broken (What a coincidence!) and cannot be established again even i unpair and pair. Beside, the Bluetooth seems not responsive when i tried to disable it.
As a veteran Linux guy, i switched to the terminal and typed the following command:
killall blued
This helped the daemon to restart itself (watchdog starts it again)
