Learn English – Word for the realisation that you are alive

I think the word wistful captures that sense of wishing for something, tinged with regret. I'm not sure that nostalgia requires you to have experienced the thing you're missing, but it does require it to be in the past. Wistfulness doesn't - I can feel wistful thinking of something I could be doing, or had once thought I would be doing by now, and neither of those fits nostalgia.

1. I've been through a lot in my life and turned me into a fighter.

2. The experience determined the very things that didn't kill me but made me stronger.

There are connotations here of ORDEAL, TRIAL, TESTING, and of a process of distillation, in the sense of separating or extracting the essential and vital elements within, and of a refining process, in the sense of being purified of what is coarse, debasing, or superfluous, again it is a reduction to what is essential, vital, true and strong.

This is the purpose of the alchemist's retort, and of the crucible.

3. These ordeals were my crucible."

CRUCIBLE noun: 2. a. An extremely difficult experience or situation; a severe test or trial: "the emotional crucible of a wartime deployment" (Kristin Henderson). See synonyms at trial. see, The Free Dictionary