4 months fall asleep during spoon feed

Pa

Hi, my girl usually takes 8oz of milk by bottle. She just turned 4 months, got her vaccines yesterday. Doctor said to mix formula with baby rice cereal now. This morning we did that, she had about 8 spoons then fell asleep in my arms. Couldn’t get her to wake up. Any tips? Im trying to spoon feed her twice a day, morning and night time as directed by her pediatrician. Im worried she doesn’t get enough to eat.