The 27-year-old says he made the decision after being told he needed to undergo surgery in an interview with Gary Neville on The Overlap.
"I got addicted to sleeping tablets, it's a problem not only I have. It's going around more than people realise in football," he said.
"Now is probably the right time to tell people. It's tough to talk about it as it's quite recent and something I've hid for a long time and I'm scared to talk about.
"When I came back from Turkey I came back and found out I needed an operation. I was in a bad place mentally. I decided to go to a modern rehab facility that deals with addiction and mental health and trauma. I felt it was time for me.
"You can't be told to go there, you have to make the decision yourself. I was in a bad cycle. I was relying on things that were doing me harm. I was waking up every day, winning the fight going into training every day smiling - willing to show I was happy.
"There is a stigma around it and it's something people don't want to do. Going into rehab is scary but I could never have imagined how much I would get from it. I was in a bad place. A lot happened to me when I was younger that I couldn't understand and I was doing stupid things that I blame myself for.
"Going there and learning about it, it was never really under my control. Understanding learning it has helped. I let go of some bad feelings I was holding which was slowing me down."
Dele also spoke at length about his mental health struggles and his difficult upbringing. The midfielder revealed he once felt like he wanted to retire at the age of 24 after being dropped by Jose Mourinho at Tottenham.
"Probably the saddest moment for me, was when Mourinho was manager, I think I was 24. I remember there was one session, like one morning I woke up and I had to go to training - this is when he'd stopped playing me - and I was in a bad place," he explained.
"I remember just looking in the mirror - I mean it sounds dramatic but I was literally staring in the mirror - and I was asking if I could retire now, at 24, doing the thing I love. For me, that was heartbreaking to even have had that thought at 24, to want to retire. That hurt me a lot, that was another thing that I had to carry."
Mourinho famously branded Dele as "lazy" in an Amazon documentary. The former England international says the Roma boss subsequently said sorry but the apology was not shown in the programme.
"He called me lazy – that was the day after recovery day. A week later, he apologised to me for calling me lazy because he'd seen me actually train and play. But that wasn't in the documentary, and no one spoke up about that because it was only me and him," he said.
"In the team meeting, he called me lazy but then one on one, I think it was on the pitch, he apologised for it. And I didn't think anything of it at the time because I know myself – I'm not lazy.
"What you see sometimes isn't the way it really is. I think, especially now with social media and all these things, we can really portray something that isn't real. After that, I think people definitely tried to use that, for some other decisions.
"I think other coaches maybe, for other reasons why I weren't playing, they stuck to that – lazy one – because it was kind of an easy one to use. And the problem was probably more than that."
Dele also opened up on his brutal upbringing and the difficulties he has experienced throughout his life, saying he hoped he could help others who have experienced similar issues.