[…] Here’s my take: You can look at it a few ways.

First, I’ll be clear in stating my opinion that Dom’s top didn’t stop spinning at the very end of the film. I’ve heard some people say that it falls right before the cut to black, but it doesn’t. This is a brilliant editing choice that takes advantage of a happy accident. Right before the film cuts to the end credits, the top is seen faltering, but recovers and keeps spinning. It most certainly doesn’t stop spinning, and leaves open the possibility that it will either stop spinning soon, or never stop spinning.

However, if you keep track of how Dom spins the top in previous segments of “reality”, you’ll notice that it falls over relatively quickly, much faster than we see it spin for at the end of the film. This leads us to conclude that, because it’s been spinning for a much longer time at the end of the film, that it won’t stop anytime soon.

So, this means that we leave Cobb in a dream. But how?

Well, in my opinion, there are two ways to look at that. The first is, he never escaped limbo and died, entering what could be considered “heaven.” He’s still physically on the plane, but brain dead, left in a coma, and eventually deceased. This would make sense, since we never actually see him or Saito leave limbo.

But then there’s the theory that the entire film could have been a big con to get Cobb to let go of his past guilt, which would mean that none of the film is real, and it’s all been played out inside Dom’s head the entire time. This would make sense because none of the other characters are nearly as well developed as Cobb, suggesting that maybe none of them are real, and the entire journey that Cobb endures could have been for his benefit, not Saito’s. 

Think about it in terms of Cobb’s history, and how his mind affects the upper levels of the dreams in the climax. How could the train and Mal be infiltrating other people’s dreams if they weren’t in Cobb’s head? Cobb states that the projections within a dreamer’s mind are embodiments of their subconscious, so maybe that’s a hint that all of Cobb’s team are part of his mind trying to get him to let go of Mal, and Mal and all of the projections out to kill him and his team are the part of his subconscious fighting the urge to let go.

If you’ll notice, Cobb’s subconscious is the only one that can affect other dreamers’ dreams. None of the other team members bring anything but their own consciousness and special skills. To me, this means that they ARE part of the subconscious, perhaps the intellectual side fighting the emotional side.

So, if that’s the case, then the inception would be in order for Dom to release his guilt about allowing Mal to commit suicide and going on the run, keeping him away from his children… or it could mean that the whole idea of going on the run was a fabricated trick of his mind- even Mal tells him in a flashback that the idea of corporations sending hit men after him is ludicrous.

What’s that you say? What about the top? It stopped spinning before in what Dom thought of as “reality”, so how can it have done that if he was in a dream the whole time? Wouldn’t it have kept spinning to infinity?

Well, no. Cobb says that the concept of a totem was Mal’s idea. Since we don’t know when the idea was conceived, it’s very possible that it is a flawed concept. The idea is that it’s like pinching yourself to wake up, but as we saw in the flashbacks to Dom’s dark past, Mal’s totem didn’t keep her from believing that she was dreaming, and that was when it stopped spinning. So, maybe it’s possible for the dream to be so real that your totem lies to you. But then, wouldn’t that make the ending even more ambiguous? Well, yes, and that’s the fun of it!

Personally, this is the ending I chose to believe.