If there's some important time by when I need to wake up (flight/train to catch, or waking up to travel by car or go for an appointment) I wake up around 5-10 minutes before my alarm. Like, always. I wish I was joking.
I am a very heavy sleeper. But I have no idea what happens to my internal clock at moments like those.
I'm from a country where English isn't the primary language, people tend to find many aspects of English complex