The defender expressed how great he felt to be back in action in the midst of pre-season after a long spell on the sidelines
The Serbian, 25, made only 10 Bundesliga appearances last season after rupturing a cruciate knee ligament in November 2013 and has been working his way back to match fitness in pre-season.
"Emotionally, I cannot compare the first day back at training with anything else," Subotic told reporters.
"After an eight-month break to play four against two and to have so much fun... This must be what it is like to be a 10-year-old boy in Disneyland!
"I will not be affected by small fitness problems. I need to make an extra effort in training. I'm still not at 100 per cent, but that is indeed rare.
"I can now run, sprint and you can throw me into duels on the pitch without any feelings of anxiety. I am now four weeks into training - I no longer think of my knee as a problem."
In Subotic's absence last season, Sokratis Papastathopoulos stepped up to partner Mats Hummels in the BVB back four and the recovering defender is relieved that Jurgen Klopp did not rush into the transfer market to buy second-rate cover.
"I would have been annoyed if BVB had fetched some cheap central defender in," he added. "We have Mats Hummels - now a world champion and one of the best players at the World Cup.
"Sokratis also played phenomenal in his first year for BVB. Such competition is great for us all."
Dortmund supplied four players for World Cup 2014 winners Germany - Roman Weidenfeller, Mats Hummels, Erik Durm and Kevin Grosskreutz - and Subotic is thrilled for his Bundesliga team-mates.
"I was insanely happy for them," he added. "I cannot imagine how amazing it must have been for them.
"I was so proud that these guys belong to us and that they have won the trophy. There was indeed a lot of joy from all BVB supporters. They deserve it, I am happy for them with all of my heart."