The midfielder cut ties with Manchester United to join Girona in August.
He told Voetbal International: "My role was played out at Manchester United, so at the beginning of this year I wanted to make minutes elsewhere.
"The choice for Germany seemed nice, and don't get me wrong, Eintracht Frankfurt is really a big and beautiful club, but I really was lost around there.
"I was a loan player for a few months and then it is very simple: then you just have to deliver from the first game and impress. But I just couldn't.
"I got that far, needed rhythm and a series of games, only that was simply not possible.
"The result was that I was going to drive myself crazy. I had to show what I could do in a competition, which made me do way too much and I got away from myself."
He also said: "I sat there alone in Frankfurt. My family in England, playing football did not run at all. At that time I sometimes really thought: 'What am I doing?'"
After a difficult period, Van de Beek has now regained happiness at Girona.
"I enjoy it again," he beams. "The fun, enjoying the game. That is so important and I have missed that feeling for so long. I finally feel like a footballer again.
"I think I've made more minutes this season than added up in the past four years. That says enough. The good feeling is back, I feel confidence again and the sacred fire in me has been fueled. Finally."