Has to be a mod issue.

Sounds like you downloaded a Skyrim vampire mod into Valheim by mistake. It happens……

Must be affecting it because on vanilla game, you wake up at dawn. There is probably a setting for how many hours you sleep on that mod.

I don't use mods so I cant be certain but I wanted to verify that on vanilla, you sleep until dawn.

It used to be that if you went to bed right after getting up it and before it told you the new day you could actually skip to the next morning... but have not heard of this issue before.

I would guess it is probably mod related.