When I become delusional I tend to kinda know that they aren't true. My delusions come and go, rarely lasting for more than a few days.
The horror I feel is there, even tho I know that it is impossible/isn't true, why? 
It isn't always like that tho, sometimes, maybe 25% of the time/duration of the delusion Im soooooo certain that its true. And can go to large extents to apeace or like 'fix it", like if I think I'm infested with parasites I've harmed myself very badly because "they can't survive in 100% oxygen because they're aliens and haven't gotten used to/addapted to our air. Usually my hallucinations tend to fuel my delusions, but depending on how delusional I am they act differently. If I'm full blown down into the shit they often sound extremely scared, but then when they aren't as horrified I think it's easier for me to realize that what I'm thinking isn't reasonable.