Bed bugs will bite you anyplace on your body while you are asleep. However, the most common place to be bitten by a bedbug is near the head and upper torso. The reason for this is because they can sense the carbon dioxide that you exhale. When you breathe out, about 5% of the gas is carbon dioxide. Even at this small amount, bed bugs can use it as a way to figure out where you are.
That might be the first place you notice bites, but deep bed bug infestations usually result in bites all over the body. In some cases, the bed bug is most likely to bite the closest part of the body to its nest. If bed bugs are nesting near the feet, you might notice the bites on your legs. Just because bed bugs are most likely to bite you closer to your head, don't discount bites in other places in your body.