The state or likeness of being beyond godly-- more than 'epic' or 'uber'. Being siddy denotes the possibility of any lower status than itself and can be considered the pinnacle of spiritual enlightenment or physical achievement in life; it can be compared to reaching Nirvana, one really good high, or sexual gratification.
"Did you see that movie, 300? Man, that was siddy!"
"I gotta take a siddy-dump!"