Baby’s soft spot

Meg

Just wanted to see if this has happened to anyone else. When my 5 week old baby is sat up right his top fontanelle dips in a fair bit. However when he’s laid down or on a slant etc it’s fine. Seen by a doctor yesterday who said it can sink depending on the position they are sat in, does this happen to anyone else’s baby when in certain positions? (He’s having wet & dirty nappies etc) xx