Fast bowlers Mitchell Starc and Josh Hazlewood took seven of the 10 wickets as the Australians mopped up a 120-run victory in the second, day-night Test to take a 2-0 lead in the five-Test series.
But Smith was a man under pressure heading into the final day, with questions over his decision not to enforce the follow-on while holding a 215-run first innings lead which allowed England back into the contest.
The tourists subsequently knocked over the Australians for 138, leaving them with a chance of chasing down a record 354-run victory target.
Smith gave an insight into the stresses he was under after England had clawed back and needed 178 runs with six wickets in hand to win going into the final day.
"I had to have a sleeping pill last night. It has been a pretty tough 24 hours if I'm being honest," Smith told reporters.
"It's all part of being captain of your country. You have to make difficult decisions and sometimes you're going to make the wrong decision.
"It's all part of the learning experience and hopefully I can learn something from this game."
But Smith was adamant he had made the right call not to put England back into bat on bowling-friendly conditions with the moving pink ball under the Adelaide Oval lights.
"I guess my rationale behind the decision was that we were a long way in front of the game," he said.
"If we bat reasonably well – I thought we batted pretty poorly to be honest to get to 350 -- we should be getting up over 400.
"We didn't do that but we were still a long way in front of the game and still confident. I would say that over the last day or two I have had a few different thoughts.
"I've read a lot of things. In the end, we've won the game, so it's all irrelevant."
Smith said he was conscious of protecting his star fast bowlers – Starc, Hazlewood and Pat Cummins – who have a history of injuries, with the series still alive and three Tests remaining.
"We know it's a long summer and I think our bowlers are very valuable," Smith added.
"Giving these guys a little bit of a rest, it always makes me confident they can come back day in, day out and do the job we need them to do.
"We also wanted to keep the England bowlers bowling. They bowled 150 overs in the first innings.
"An Ashes series is long and if you can tire their bowlers early in the series then it can make a big difference at the back end. That was also part of it."
Smith also said he was "switched on" during prolonged sledging exchanges with England pace pair James Anderson and Stuart Broad while he was batting in Australia's first innings.
Anderson later boasted that Smith had been rattled by the sledging, but Smith took the opposite view.
"I think they actually switched me on to be perfectly honest with you," he said.
"I enjoyed it. It made me really focused. It got me in my little bubble and it got me going."