When dealing with a patient who you suspect of having a spinal injury like someone who has fallen out if a tree and you are on your own you need to get help but you also you need to keep the person safe. The problem you have to leave them to get help but if you leave them on their back, they could vomit and then choke and die. If you move them, you may make their injury worse.
If there were more than just one person, you could send them for help or using more people, you can use the log roll to safety turn them.
The solution is the recovery position. You may think that the recovery position would twist their spine but if done slowly you can turn someone onto their side without twisting the spine. The whole time you move them, think about what you are doing and make sure you do not twist the spine which could make their injury worse. It's a good idea to practice this skill a few times as it does take a few goes to get it right.
Once you have moved them, ensure they are breathing and their airway is open. Talk to them the whole time as even though they are unconscious they may still hear you which is reassuring. Then go for help. If they vomit, they will not choke and they should stay in that position.
When you return, recheck their breathing and cover them with a blanket to keep them warm. Keep reassuring them until help arrives. Tell the EMS what has happened and what signs you have seen and if they were conscious, what symptoms did they tell you.