Merry Christmas kitties and slaves! 
So in todays instalment of random illnesses my cats have (the other one has hyperestesia and a few weeks ago this one had a random skin growth on one of her beans) we have vomiting foamy clear fluid at 4am. This has happened for 4 nights in a row now. She’s perfectly fine otherwise - eating/drinking/pooing/causing chaos wherever she goes. There’s no fur in it and she’s not one for hairballs so I don’t think it’s that. She’s up to date with worming (I have the scars to prove it). Google suggests something called bilious vomiting syndrome due to having an empty stomach so we’ll try some Christmas chicken at bedtime tonight and see how we get on. I am obviously reluctant to go to the vets on Christmas Day and she seems so well otherwise!
Just to add - she eats Blink/Rosie’s Farm and Lily’s Kitchen for wet, and Purizon for dry so no grain. I can’t leave dry down all the time because the other cat gets a bit chonky if she has free access to food.
Any ideas?