Sneijder, 36, retired from professional football in 2019 after a career that spanned nearly two decades and produced 20 major titles.
Despite being considered as one of the greatest talents of his generation, the 134-time capped Netherlands legend lamented the unprofessional lifestyle that saw him shipped out of Real after just two seasons.
"I was young and I liked success and to be the centre of attention," Sneijder opened up in his autobiography that's set to be released on Friday.
"But bad things happened there. It wasn't drugs, but alcohol...I got used to living like a star. You're adored as a Real Madrid and going out on the street spending thousands of euros and paying for things for people.
"I can't say that I was deprived of anything. I played pretty well, but it was said that I could have done even better.
"I stayed alone and I saw little Jessey very little. I could only be alone... and I didn't realise that the bottle of vodka had become my best friend.
"Physically, I didn't realise. I would get up the next day as if nothing had happened. I kept training but getting worse each time and clearly less focused.
"I lied to myself, saying that everything was going fine and took refuge in my footballing intelligence. I sank physically. I ran less, I hid from my coach more. I also thought that nobody would notice."
Sneijder scored 152 goals and registered 143 assists in 573 club games over his career with AFC Ajax, Los Blancos, Internazionale, Galatasaray, OGC Nice and Al Gharafa.