Pietersen has also defended the rash shot that brought about his dismissal on day two of the Boxing Day Test, saying when it came to public opinion he could not win.
After winning the home Ashes series 3-0 this year, England have lost the urn by the same margin in Australia.
The Boxing Day Test so far has been their best performance of this tour.
At lunch on day three they had an overall lead of 105 with 10 wickets in hand.
"People shouldn't forget, and it's never been done before, that guys have got to go and endure 10 back-to-back Ashes Test matches," Pietersen told Sky Sports.
"I've been told that a number of Olympic athletes go into some sort of post-Olympic depression or a negative frame of mind.
"I'm not saying we're in a depression or a negative frame of mind, but after you've competed at such a level, post that competition, mentally you're a bit fragile.
"To play an Ashes then another Ashes, and for us being away from home, it's a tough gig.
"It's been an incredibly pressurised situation."
Adding to England's woes, two senior players have left during the tour.
Jonathan Trott went home because of personal issues and Graeme Swann suddenly retired in the lead-up to Melbourne.
Pietersen has also been a lightning rod for criticism in the midst of England's troubles.
Most recently, he was pilloried for attempting a wild slog early on day two, only for Mitchell Johnson to bowl him for 71.
English great Geoff Boycott has also called him a mug ahead of this Test.
"This game is a great leveller," Pietersen said.
"If you start believing people when they say you're great it's going to hurt you.
"If you start believing people when they call you a mug that's also going to hurt you.
"We just want to try and salvage some pride. We want to try and turn things around."
Pietersen also said he was well aware of the reaction to his day-two dismissal.
"I know it's a bit of a talking point," Pietersen said.
"I don't know what the numbers are on our tail, but as soon as (Tim) Bresnan got out, I was under the impression that I had to do all the scoring and take all the strike.
"Look, I get out for nought, I get nailed. I get out for 70 ... I was playing for the team's cause to try and score as many runs as possible as quick as possible because I knew I was going to have to do it."