I was under the impression that limbo was a separate level entered into when you "die" in a dream but your body is not ready to receive you back. Saito goes the

I was under the impression that limbo was a separate level entered into when you "die" in a dream but your body is not ready to receive you back. Saito goes there when he dies in Level 3, and Cobb when he drowns in Level 2 because he's trapped "below". Level 4 was simply a deeper level filled by Cobb's dream world that he had created with his wife. I might have misunderstood though.