she smiles - edit4

[wasellajam]

Hi, I appreciate your attempt to capture this, for me it is on the verge of success. Some notes:

she smiles
and feeling so relieved
in that warm swift moment
I must cry except
it’s gone before my tears can well
It took me a while to parse this, I kept applying "relieved" to "she". Strong breaks throughout.

then terror strains and locks.  Not a fan of "strains".
her features back with knowing  Maybe lose "with" and drop "knowing" to the next line.
only that she cannot understand
or put a name to anything she sees
You clearly don't want punctuation for this but maybe try it to help you see how it should read, then remove it.

dementia’s not damnation "damnation' works so well below maybe you can lose it here, maybe just "dementia fades".
for it fades
into waking unconsciousness
with its heartbreaking smile
until tension   "tension crippled" isn't working for me, both sonically and meaning.
crippled mindfulness
and fears return   Possibly "fear returns".

not damnation
since neither deserved
nor endless.  Super ending.

I think this is an important poem, there is nothing worse than those moments of almost clarity. You might head in that direction for a title.
You're very close to portraying what feels indescribable. Kudos, thanks for posting it.