Tumbling out of bed

Aiden had his first tumble out of bed last night. He woke up crying at 1:30am...a nightmare, we suspect. Erik got him to go back to sleep pretty quickly. He woke again at 3:30am (these nighttime wakings are VERY rare). This time I went to check on him. He was sitting on the floor next to his bed looking very confused. I put him back in bed and sang him a song, holding his hand. He fell right to sleep as I was singing to him. This morning, he didn't even seem to remember anything. I am amazed that he could fall out of bed past the railing. He must have been sleeping right at the very bottom of the bed. When I check on him at night, he is frequently lying across his bed; it is always so funny to see.