The 23-year-old made 33 league appearances on the way to helping Jurgen Klopp's men successfully defend their Bundesliga title last term, before spending the summer helping Germany to the semi-finals of the European finals.
"After Euro 2012, I had very little holiday and almost no desire to play football," Hummels recalled to Bild. "I was slipping into depression, from all the travelling.
"Even if I deliberately tried to focus on other things, I got angry after games like those against Frankfurt and Hamburg. I felt responsible for several of the goals we conceded.
"The team have had their problems, even many, in fact. But they've always been there – we've not won our titles without obstacles."
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"I feel I'm coming back to the game however. The 5-0 win was a start. Now, it's important we put this mini-crisis behind us and get back to form.
"Bayern Munich are having an impressive season, but we were eight points behind them last time around, and were still champions."