Strictly Sleep Eating?

Anybody having issues with their kiddo only eating in their sleep? My nugget wouldn't hardly eat anything the first 2 months, but we could get him to eat when he was sleeping. Pediatrician said just feed him while he's sleeping so he can start gaining weight finally. Fast-forward to almost 6mo next week and he still refuses to take any formula while he's awake. He takes solids while he's awake just fine, absolutely loves it! Just cannot get him to take formula awake at all. Not from a bottle or a sippy cup. We're checking in with his doc next week at his 6mo appt but it's starting to make me nervous. Anyone else have this issue or know someone who had it?