I got the impression Sidious enginered that, he wanted Anakin to attack Windu.
One moment he is crying weakness, the next he unleashes force lightning whilst grinning and saying something like absolute power.
He had left himself in positions of weakness before, like where Anakin had his lightsabre drawn on him and Sidious feigned being unharmed and at Anakins mercy.
Sidious was not just powerful, he was devious and fooled the jedi order and republic with ease.