What are you talking back, when Palpatine met up with Dooku at the end of Episode 2, before Palpatine used lightning on Mace, he had the same face and voice! And when Mace blocked the ligthning, Palpatine wasn't going weaker! He was all lying to make Anakin kill Mace, so he could get closer to the dark side! You see that because when Anakin cuts off MAces arm, Palpatine starts laughing, and uses his force lightning again!!
All he was doing is coming back to his original form!