Is it ok not to place headers on pages?

Do I need a header on the top of every page I have or is a prominent indication of category in the sidebar enough? I keep jumping back and forth and cannot come up with a permanent solution. It also affects a few later parts of the project - due to consistency, so I am a bit struggling, because on some pages it seems ok and on some something seems missing.

I'd like to leave them out, but is it ok for sure not to give the user the indication on the top of the page, just in the sidebar?

This site right here does it - when you go to the user's page (yours or someone else's) there are tabs on the top, but the main content is below, with the name and the rest of the info. And I think it's easy to use.