Based on extensive notes from a previously unknown draft of 'Star Wars', I believe that by 'tremor' GL meant to imply that Darth had indigestion. He often used to eat Obi-Wan's cooking and had the same feeling- so therefore the reference originally WAS about Obi-Wan.

The 'circle' he refers to being 'complete' was actually an Imperial version of Alka-Seltzer.

On a side note, continuing GL's wonderful Jedi naming trend, he re-used that idea and if you read the credits of AOTC there is a Jedi named Salka-Eltzer.