It is like looking after a kid, but in reverse. They become progressively less of who / what you knew them as until they are gone.
I don't know how your health system works, but if is anything like ours, please make sure that the psych evaluation gets done FAST. Here, the clock doesn't start on a bed placement until you get past that hurdle - and please don't let anyone try to send you on a guilt trip for trying to do the best for your family. The worst part of this is the effect that the 36 hour day (not a mistype) needed to care for someone like this has on you as the carer - especially when you think that you are coping. Please listen to those around you: sometimes a reality check from someone not too close is in order.
Yes, there are things that you laugh at - and then feel bad about. Don't worry, others have been there as well, and it's not any failing on your part. I can still remember my dad (with dementia) climbing a tree to trim it and not being able to get down again. I see my wife's mother being a mirror of her mischievious 4 yo granddaugher in her behaviour. It's all part of the journey.
I have been thinking of you and the frustrations / concerns / dissappointments that you are having and really hope that there is a positive turn around for you real soon.