Like you get transported into an alternate universe where everything is almost same, but with tiny differences. The world looks normal to everyone and you’re the only one that have memories of the differences.
Do you think you would trust your memories or would you think you lost your mind?
and it’s for exactly this reason that arguing with a delusion strengthens it. If you show a person with Cotard delusions how to find their pulse they’ll come to the conclusion that dead bodies can still have a heartbeat and if you show a person with capgras delusions a DNA test now the doppelgangers can mimic DNA too. the new information just gets integrated in a way that supports the delusion. all you can do is try to distract them while the antipsychotics hit and try to keep them socially connected through unrelated stuff like hobbies, music, etc.