Petrosianic: <Seriously Spassky says he and his team ( Bondaresky ? etc ) went fishing , he got sunstroke ( stupid ) and then did not request a sick break ( stupid ? )>
LOL. I've never heard that one before, and I tend to doubt it, as Spassky wasn't an habitual excuse maker, like many GM's.
But Petrosian wrote about the game, agreeing with part of what you said: that it was a mistake not taking a time out after winning Game 19. According to him, when you've been chasing a player for a long time, there's a psychological turning point at the moment you succeed in catching him, where you need to take stock and readjust your bearings to the new situation.
We can see the same thing in several other instances. Namely:
1) Karpov-Korchnoi, 1978. Korchnoi had been chasing Karpov since Game 13, finally equalized in Game 31, and then lost the very next game.
2) Petrosian-Botvinnik, 1963: Botvinnik had been chasing since Game 7, tied the match in Game 14, and then dropped the very next game.
3) Botvinnik-Smyslov, 1954: Smyslov was down 3 points after 4 games, went into slugfest mode, and actually succeeded in taking the lead before mid-match, but remained in slugfest mode, and lost it again. It was time to readjust the strategy after catching up.
4) Even the famous Fischer-Petrosian 4 Queens game, when Petrosian had been on the defensive a long time, but took a draw at the end when he was standing better. According to Fischer, he was "unable to readjust his frame of mind and start playing for a win." Same thing as the other examples.
According to Petrosian, Spassky was hoping for a quiet draw in Game 20 to rest up before making another big effort to take the lead in Game 21, with White. Ergo, he resolved to go all out for the win in Game 20, trusting that Spassky wouldn't be psychologically prepared for it. He wasn't. Taking a time-out might have helped a little.