I believe it to be one of the tales comics, or possibly even one of the Clone Wars comics, but there was one of palpatine practising -and this is only what it appeared to be to me, I could be wrong - battle meditation. Influencing the war and creating a much larger darkness in the force that was making it harder and harder for the Jedi.
Even Mace Windu said in AOTC "Our ability to use the force has diminished".
So yes, Jolly, Palpatine probably did a lot of Sith stuff whilst no one else was around. Plus, he had to keep his knowledge of the force and his ability to use it secret. Not good if Jedi got wind of it.