You know, sometimes your parents are caught up in more important things than waking you up. They could have been busy doing something else and had just forgotten to wake you up.
Also, if you went a full 12 hours of sleeping that must have meant you were tired. They could have tried waking you up, but you just fell back asleep and forgot about them waking you up.
One time my dad had woken me up from our living room couch and I had walked all the way downstairs to my bedroom and didn't even know until my dad told me the next day.