A reality feeling is what you get when something feels real. The realization sets in — whatever this thing is, you've got a real feeling that it's actually happening.

実感 means a realization that comes from lived experience. For example, when you're expecting a baby, you may understand that you're becoming a parent, but not truly have that realization until the baby is born or you hold them in your arms. It's the sense of something feeling real beyond theory or explanation — when it truly sinks in.

This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. The reading for 実 gets changed to じっ so be careful!