I know what you mean by just randomly becoming aware that you are dreaming without any reality checks or such. It happens to me too even though I'm still fairly inexperienced. You build up awareness while dreaming, then start noticing the dream-like elements of the dream and just like that you know you're dreaming. I also agree with Gab, it has much to do with training your awareness during waking life. I recall King Yoshi having a good tutorial about it.

I still do reality checks throughout the day though. A lot of times having become lucid, after a while you seem to start losing control of the dream, so reality checks make you become more aware and help you get more control. That's for me at least.