His lumbar spine (low back) is arched backwards which approximates his joints and basically squishes them together. His neck is in an even worse position - arched backwards and forced into full rotation. This man slept like this for at least an hour and I'm pretty sure he would not have felt good when he woke up.
Forcing your joints into these positions is not good for them! Our joints like space - prolonged extension (arching backwards) causes the joint surfaces to come closer together, this squeezes out the joint fluid and leads to irritation.
This mans position is an extreme example of what happens when you sleep on your front (unless you use 2+ pillows, which you need to stop, now!). Even if you wake up in the morning and don't feel stiff in your neck or low back, which is unlikely, you could be causing problems for yourself in the future. Potentially a lack of nutrition to your joints, caused by prolonged extension, could lead to the development of early wear and tear.
So can you change? Yes! Our sleeping position is a habit and we can change it! Try going to sleep on your side and put pillows in front of your body so that if you try to roll onto your front the pillows will stop you. Another, more extreme, method is to tape a beer bottle cap to your belly button (stay with me!) so if you lie on your back or side you are fine but if you roll onto your front the bottle cap will dig into you, causing you to wake up and change position.
Changing your sleeping position is such an easy way to protect your spine and may prevent a few trips to your osteopath!
