Why when I get up very early do I have a headache all day?

[Spaggybollynese]

It also happens if I have any semblance of a ‘lie in’ - makes eg travel, holidays not fun!! What is this about?

Dehydration ??

Dehydration also my guess.

Opened the post to say dehydration too!

Why would I be more dehydrated getting up at 5 than 6 though… ?

Good point but I suppose if you get up early your day will be longer and possibly your liquid intake the same as for a shorter day.
But if it's only an hour then I agree, it seems odd that it makes a difference.
Trying to be delicate here but could it throw your toileting habits out ?
I get a headache if I've not opened my bowels as they say in hospital.