can be all sorts. even things like certain diets, last meal of day can cause sleep issues.
I tend to wake up naturally around 3-4am each day, even at the weekend, but I'm usually asleep by 10 so not end of the world. II exceercise most days first thing whilst fasted, so its not exercise late in the evening causing my 'issues'.
yes sleep is important, but not everyone needs 8 hours. books like that Walker one are no doubt useful for many, but can also cause anxiety for some around thinking they're not getting enough, when it's not always the case. In faact I'd hate to be getting 8 hours + , as I wouldn;t have enough time in my day! and no, I don;t think getting those 2 extra hours or so would make me more productive. I can get a lot done in an extra 14 or so hours a week, 48 a month etc.
I'm 41, look young for my age, single digit body fat, exercise intensely most days etc. I also have quarterly private blood tests that cover pretty much everything from blood cells, organs, vitamin levels, test levels etc and so far everything is healthy.
Caused me concern, slight anxiety for years as everyone says 'you must get 8 hours', but there are reports out there that thats not always the case. I think it also helps a good deal if your diet is on point and no doubt genetics play a part.
If everything is healthy - diet, exercise and you don;t feel like ****, I wouldn't worry too much tbh. In fact I embrace it, as gives me opportunity to get a lot of stuff done whilst most are sleeping. You may find you sleep less most days, then have the odd day where you sleep an extra hour or 2 naturally.