Any tips on how to undementor a dementor
Arguing with a dementor is pointless. They get paranoid and protective and extra defensive of their anxiety even more when you point out they are wrong. They're coming from an emotional place, not a rational place, so meeting them with facts is useless because they dont care about facts. They are getting an emotional payoff from their hysteria and wont give that up easily.
The best way ive found is to agree with them. Eg "yes- I think you should stay in for the next 2 years. Very wise. I'll be going out next week but you should definitely stay in until 2022 just in case. I'll see you in two years time then- bye!" At that point you can see them visibly deflate a bit.
Then, wait and see what happens! I can guarantee you they wont go through with it because deep down they know its utterly ridiculous but they are enjoying the drama too much to let it go right now.