Baby movements

Dallas

Hey guys! I’m 18w6d today. Last week right as I was almost asleep (on my side) I felt some movements or quickening but haven’t felt it again since. I was lying very still and on the side I felt movement but it’s worried me I haven’t felt anything since. I work in ultrasound (but on hearts) but I still can see my little man in on my machine and he’s very active actually! Why can’t I feel him? I’m not overweight and have a normal body type.