I think the effects of a perfect game or no-no also can be physical. I mean it's a guaranteed complete game and guys often extend to 125+ pitches to get it done where if they were winning 5-0 having given up a single hit they might be pulled around 100. Plus obviously the mental strain of throwing a once in a lifetime game can lead to a guy putting a lot extra on late inning pitches and stress the system even more.
I mean a guy with a 10-0 lead having given up a hit or two is throwing get me over fastballs late in the game just to finish a complete game, but with a major achievement on the line, they are still letting it fly late with a high pitch count. I've felt this way for a while. It's more obvious for older pitchers I think.
I remember when Buehrle threw his perfect game and then came back and started the next game with like 5.2 innings of perfection. Then suddenly he hit the wall and the next 4-5 games (IIRC) he struggled. I thought it was the stress from all those tough pitches.
Riding shotgun on the Sox bandwagon since before there was an Internet...