I overslept and I missed the class. (IF ...)
If I hadn't overslept, I wouldn't have missed the class.
I asked for an upgrade and now I'm in 1st class! (IF ...)
If I hadn't asked for an upgrade, I wouldn't be in 1st class (now).
I worked at a restaurant in Japan, and I'm a sushi chef today. (IF ...)
If I hadn't worked at a restaurant in Japan, I wouldn't/might not be a sushi chef today.