I haven't been in this sleepless state for too long, awaiting a new era. I only have three bullets next to me. And a gun, which I am not sure will be useful to me.
I am most familiar with the phrase "estar en vela" to mean "mourning."
In this text however, I simply used "losing sleep" since it's not clear whether or not the "speaker" has a reason to mourn. He could be losing sleep for other reasons.
"Estar en vela" definitely doesn't mean "mourning". It means here "being alert or vigilant" and thence deprived from sleeping, as the general meaning is "being wakeful".
Our character seems to be vigilant because he is looking forward to fighting for the arrival of a new era and he wants to be ready.