Boycat has recently started to vanish somewhere in the house (no idea where) and sleep right through supper and beyond. He only appears just as I'm going to bed on those nights - possibly for the bed time Dreamies they usually get. Rustling the Dreamies packet loudly may bring him out from wherever he is?
The other thing that mine do, Boycat especially, is if they feel under the weather or something has scared them they tuck themselves under the sofa, or even inside the covers at the back. I can't use the recliner on the sofa in rain storms unless I can be sure I can see both cats, so they can't get trapped in the mechanism.