Falling Asleep While Nursing

Last night I was nursing my baby in bed like I always do. According to my husband I had fallen asleep at some point while nursing. Our daughter apparently rolled off of me and was laying face down on the bed screaming. He woke up and picked her up and handed her back to me. I don't remember him handing our daughter back to me. I do remember waking up at 3 a.m. with our daughter on my chest and laying her down beside me. I'm usually a light sleeper and wake easily. How can I avoid another incident like this? She sleeps the best in bed with me and my husband.