How does the NHI breath?

One thing I am always wondering about, do the NHI breath oxygen like us?

How come they can come from space to our atmosphere and in the oceans seemingly without any spacesuits of whatever. Do they breath oxygen? Do they breath at all?

Have they found any life support systems in the crash retrievals?

And also what do they eat? Do they need sleep at all? Don’t they have to go to the bathroom?

So they travel al these lightyears without any life support? I don’t understand how that is possible.

I never see any posts about the practical stuff about interstellar travel.