Baby fell asleep when feeding

My baby fell asleep many times during feeding. Sometimes she don't wake up even burp her or shake her gently to wake her up. In the end, I have to pour away the milk and it's such a wastage. If I don't feed her, she will cry. But I admit sometimes I can't tell if she is hungry or just cranky and want to sleep. What should I do? Is this normal?#pleasehelp #FTM