The midfielder is on a straight loan at Bayer this season.
"There were a lot of times when things were very good and you enjoy every part of it," he said before Leverkusen's Champions League trip to Atletico Madrid on Wednesday. "And there were times and you think, 'what have I done wrong? Or what am I doing wrong not to be playing?'
"Sometimes it was difficult and frustrating. You are sitting on the bench or might not even be in the squad and then you're like 'what on earth have I done to deserve that?'
"I train well every day, I give my all in every game, but then I don't get picked. Of course if there are other players doing well in your position, they should get picked as well, but at the same time, you always want to fight for your position and have a fair chance."
Hudson-Odoi is yet to have a conversation with new Blues boss Graham Potter, who has enjoyed an unbeaten start to his reign. The winger's Chelsea contract lasts until the summer of 2024, only a year after the Leverkusen loan ends.
He told BBC Sport: "I don't know what the future holds. Obviously, at the end of the season I'll go back to Chelsea regardless and we'll see what happens from there. That's where I've always been since I was a kid.
"I always look at stuff as a learning curve, never negative. It's always a learning factor for what you do next time.
"My main focus right now is being here and helping the team as much as possible. I don't see that far down the line yet."