What Does A Sleep Center Use So Many Cameras?

American Sleep Medicine has cameras to monitor people undergoing sleep studies. To the best of my knowledge each room has three cameras. A bullet camera with integrated IR, next to a dome camera which are both mounted opposite the bed. There is a third camera about face height at the doorway that looks similar to a flip cam. I'm sure they use at least one of these to record what you're doing in your sleep. It probably comes in handy for sleep disorders that cause sleep walking or people to fall out of bed, but I can't figure out what the other two would be used for. Can anyone who has installed at a sleep center provide some insight?

Here's a photo of the two on the ceiling: