In the movie Inception, at the end, when Cobb goes to limbo to rescue Saito he starts to forget "reality" and he has only been there for like 10 - 15 minutes. However, he spends decades with Mal in limbo, but still somehow remembers that this world isn't real. Also, both Cobb and Ariadne act completly normal in limbo during Fischer rescue. This is weird, escpecially for a first - timer like Ariadne. Shouldn't they lose sense of reality almost instantly just like Cobb did in Saito rescue scene?
There are two limbos. Or two ways to enter it, depends on your perspective.
Stealing from this answer,
[Cobb] goes down using the machine to get Fischer. Here they both are aware of where they are and what they are here to do.
Once Cobb dies [by drowning], he reaches Limbo for the second time (the opening scene). This time around he's died and reached Limbo, hence he has no clear idea as to where he is and how he got there.
When Cobb and Mal were in limbo for decades, they didn't die, just went too deep, so they remembered (for a while). When Ariadne and Cobb go there, also on purpose, they also remember. When Saito and Cobb actually die, it's much more hazy and confusing.