1: agonisante
dying. Refers to the "death agony."

2: allégée
P.part. of alléger, to lighten (a load), to relieve, to alleviate.

3: sembla
Note that although most of the verbs in this passage are in the imperfect tense, there are a few, like this one, in the simple past. Think about this and see to what extent you can preserve this distinction in your translation.

4: vapeur
here doesn't have its usual meaning of "steam"; think of something more appropriate.

5: aspergea
simple past of asperger (de) - to spray or sprinkle (with)

6: ciboire
ciborium or pyx, a container use for the Eucharistic wafer (Host).

7: défaillant
In addition to its standard meaning of "to fail, to become feeble," défaillir also has a medical usage: to faint, to swoon.

8: séraphiques
angelic. Refers to the seraphim, an order of angels.

9: si bien qu'à présent
The key phrase here is not bien que (although), but rather si bien que (so much so that, such that). Note that it is not followed by the subjunctive.

10: courbatue d'orgueil
literally, bent over with pride.

11: entrevit
simple past of entrevoir, to glimpse.