After smashing finals contenders Collingwood just eight days earlier, the Lions were brought back to earth with a 58-point thud by the Dockers at the Gabba.
Leppitsch said Fremantle had beaten his team psychologically as much as it had with its manic pressure.
Despite having more of the ball than their opponents, the Lions turned it over regularly in the first two quarters and were made to pay a heavy price.
Leppitsch said his team was "shocked" at the start of the game and took time to recover.
"I thought the game stepped up another notch," Leppitsch said.
"They're very alert defensively and they make you be clean with the ball and if you're not they'll get you.
"We're just that bit off at that level I think. We're not bad defensively, we've been pretty good, but it stepped it up to the top four pace today and we couldn't handle it."
Leppitsch conceded the psychological pressure the Dockers apply was hard to overcome.
Everywhere a Lion turned, there was one – and often two or three – Dockers right in their face.
The Lions panicked and tried to use handball to squirm their way out of trouble – going at a 2:1 ratio with kicks for much of the time – but just dug themselves deeper into a hole.
"It's easy to talk about it, it's easy to watch on the vision," Leppitsch said.
"We watched examples of Sam Mitchell last week panicking with the ball and he's one of the best players in the competition, so they can do it to anybody.
"They're in your face. When they man the mark they man it with intensity. They treat manning the mark like their life depends on it and that's what I want our boys to get to.
"We want to practise that, we want to get to that level. I don't think the gap's that big."
After trailing by 47 points at half-time, the Lions battled hard after the break to concede just six goals to four.
It was a far cry from their previous home match against Adelaide two weeks ago where they conceded nine final-quarter goals to lose by 105 points.
Leppitsch said the Lions' final round against Geelong next Saturday would be another "great test".
"We play two top-four teams in the last two weeks," he said.
"One, Freo, which is probably the best defensive team in that mix, and Geelong is probably one of the best offensive teams in that mix.
"We'll go from one extreme to the other so our defensive stuff needs to be good next week to curtail Geelong."
