Hi My Name Is Christina,my Fiancé Has Very Bad Popping

Hi my name is Christina,my fiancé has very bad popping I the base of his skull, when he looks down it pops severely, it's now feeling like its grinding together, maybe like bones are grinding together, is there anything I can do or he can do to ease the pain or popping!! It's popping more frequently now and is now it has this grinding feel to it!! I'm worried and would like answers!!! Thank you!! Anything can help