Active Sleep Or Fussing?

I’m a ftm so please bear with me. How do you know if baby is in active sleep verses they are fussing to wake up? My baby fusses a lot in his sleep and the best I can explain is he is grunting a lot, and fairly loudly. But when I check on him, he’s still asleep with his eyes closed and doesn’t wake. Do I wait until he’s awake or get him up? It’s not as big of a deal when he’s napping, but during the night he’s in our room and it’s hard to go back to sleep.