when you are instructed to choose and discard a card from your hand, can you choose a Whispers in your Head card? Feels wrong but I can't locate anything that says you can not do this.
For example, the Forced effect on the Mess Hall, or Wendy's ability.
rules: whispers in your head + discards (minor spoilers for U. Oath)
"A hidden card counts toward your hand size, but it cannot be discarded from your hand by any means except those described on the card."
From https://arkhamdb.com/rules#Hidden
Edited by Network57Wrong copypasta
49 minutes ago, Network57 said:From https://arkhamdb.com/rules#Hidden
Originally printed in the Path to Carcosa campaign guide, in case there's any doubt as to officialprovenance. 
They cannot even be discarded randomly, per the quote.
Edited by Khudzlin14 hours ago, Khudzlin said:They cannot even be discarded randomly, per the quote.
Which makes sense since they have a different back. It's more like it's actually in your encounter area, but affects you like it's in your hand, so you keep it there for convenience.
I think of hidden cards as having all of the negatives of a weakness in your threat area, and all of the negatives of a weakness in your hand, sort of combined:
Can I discard this randomly? No. Can I discard this when something gets discarded from play? No. Does it really count towards my hand size? Yes. Am I going mad? Probably.