The batsman was a pivotal figure as Australia retained the Ashes with a 2-2 draw in England this European summer, having compiled 774 runs across four Tests for the Baggy Green.
Focus now turns to the Australian summer, with T20 series against Pakistan and Sri Lanka over the next month, and Smith says he feels refreshed after shaking off fatigue from the Ashes campaign.
"It was probably a bit of everything: mental, emotional, physical," Smith told reporters at Sydney Airport.
"Towards the last Test match it got to day two and my mind was saying 'keep going', but my body had shut down and wouldn't let me do anything.
"I was a little bit sick after that. I've had a good couple of weeks just to lay low. I just got back into things over the past week.
"I've had three hits now. That will be enough to be ready to go for this first Shield game."
Smith will make his first appearance in domestic first-class cricket since the 2018 ball-tampering scandal when NSW face Queensland in Thursday’s Sheffield Shield clash at the GABBA.
Questions have already been posed regarding the possibility of Smith captaining the Australia side again, with his leadership ban set to expire in 2020, but the 30-year-old played down speculation and praised the work of current skipper Tim Paine.
"I'm not even thinking about that at the moment," Smith said.
"I was pretty chilled out the whole time (in England). I'm obviously pretty intense when I am out there batting but I help out wherever I can.
"I don't want to sit back and not say something if I think it might help us. We will cross that bridge later if it comes. At the moment I am comfortable and Tim is doing a great job."
Smith is expected to make a domestic return to Test action in November when Australia host Pakistan in a three-match series.
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