For me, alarms simply don’t wake me up. I’m literally unconscious and not just asleep. That being said, I only need 6 hours of sleep a night and I can’t sleep any more than that. However, I also have delayed sleep entry. So, I usually stay up until 1am and wake up at 7am, with no alarm. If I want to sleep less than six hours, I simply won’t wake up. Famously, in the military, I was dragged outside, to the morning formation, and slept through the entire thing. It was entertaining enough that I didn’t get in too much trouble, but alarms simply don’t work for me. I ended up getting doctors orders to always get six hours of sleep, if possible, instead of the 4 hour minimum. I was always worried I would sleep through important things in a war zone; and I did. I just never got caught or admitted to it.
Do you have DST where you live? Do you suddenly adjust to the new time when travelling to a different timezone?
(All this to say that you sleeping 6h flat is plausible, but times-of-day are a human, social construct, and it's impossible for your body not to be able to adapt to going to bed earlier and waking earlier)
Never had an issue with time zone changes when going east, I just stay up later and then go to sleep. Going West, however, is hard. Going to sleep more than a few hours early is quite difficult.
I think this goes to say that you could potentially adapt to going to bed earlier than 1am (eg. if the above is the only thing that works for you to modify your sleep routine, just keep staying "up later by 4h" for 5 days straight, and you'll be going to sleep at 9pm on the 6th day). If it's related to daylight/nighttime, you can move locations to where days are shorter or the TZ is more misaligned (eg. don't go to Spain or France which are largely in the wrong TZ).
My entire point is that it's likely sociological for you: you either drink your last coffee at 7pm and this keeps you awake for another 6h, or you get into a routine at a particular time, or... As in, your original claim that you "simply can't wake up at 6am" seems unrealistic since "6am" is a thing that means different things in different locations.
