when it came time to cross the threshold into space I became afraid and unable to push myself further.

Did this fear otherwise disturb the realism of the dream, or jar it somewhat? Like, were you in any way pulled back into waking conscious, even in the slightest because of it?

This was because going into space in normal reality would lead to death and because the dream felt real I was uncertain if I would die in my dream if I continued on.

That's interesting. Typically it is death in dreams that yanks us back into waking consciousness, so I find it intriguing that instinctual self-preservation was so immensely present in a lucid dream that you feared dying in something you knew to be a dream. Perhaps this suggests that in some ways at least, we feel at home with certain precepts of life, regardless of what state of consciousness or reality we currently inhabit.

the fact that I was afraid may suggest that I was quite conscious

Isn't fear a very subconsciously-rooted response tho? Like, wouldn't it be possible for one to experience it outside of complete consciousness whilst in in a dream-state?

In my experience and study alike, I have found fear to be a very natural, instinctual response to things we are otherwise unsure of, or just know inherently to be afraid of. I think the constant programming of what to associate fear with would easily transcend any dimensional limitations of one conscious state to another. Thoughts?