i was also really bad at telling the difference. with luke, i noticed that if he was fussing, i went in, and his cries escalated rapidly - i never should have gone in in the first place.
at 8 months, separation anxiety may be starting. what really helped me was to work on object permanance. when he cried, i'd go in & soothe him until he stopped (we did pat/shh cause it still worked). after he was calm, i'd turn around & leave. if (when!) he started wailing again, i'd go back & repeat. a lot. the first few days i think it took 45 minutes before he was finally satisfied & went back to sleep. but then the time started to decrease, and he went back to his normal self again.
HTH