Hi Taraz.
While you cannot envision things like you once did, your ability to describe them in great detail and paint a picture for others has only developed. Perhaps there is some comfort in this?
I understand the feelings of frustration (but I cannot begin to imagine the depth of it) you are experiencing with trying to logic why it took place and you did suffer trauma, you feel that you have lost parts of yourself which you are grieving.
Reading about your grandad was particularly sad and yet touching as I know you are now identifying with that experience you had of him completely differently than you did as a kid.
Don't lose hope, I know it may seem rich coming from me, but I witnessed someone older than you completely lose their fine motor skills, their speech, their ability to put on their own clothing, even their ability to identify what clothing was...make a recovery over time to the point where they regained almost all of their previous functions. I know that no two strokes are the same, but the brain does have amazing capabilities to reroute itself and turn on the lights in new rooms.
Keep fighting & keep writing.