I don't think you need to feel guilty, he'd call out for you if he wanted you. Maybe he just likes having a lie in and thinking about things?
I used to leave a book shoved between the cot bars and the mattress for my DS, he also had lights on a timer so he could wake up get his book and have a read for 20 mins (then his light went automatically off again) - I will do anything to get an extra 20 mins!! In my defence I didn't have a single lie in until he was 19 months old so of course I treasured 20 mins of quiet! Funny boy, at 21 months he was mid-book and his light went off so he shouted "Mummy light on again!" in a rather demanding tone! ha! He must have really meant business as it was the first time he'd ever said Mummy!
I think some kids just like to have time on their own, like adults do.