In short, by far the best way to heal your colonists in Going Medieval is to put them to sleep, no matter what's bothering them.
However, sleeping alone is not enough to completely rid them of an ouchie boo boo or injury. This is because you will also need someone to tend to the wounds for them to heal through this process.
That being said, you can effectively assign one to heal wounds by visiting the Job tab in the top left of your screen. Once this tab is open, find a settler with a beginner or high level in the upkeep skill, then click on the number until it is one.
Related: How to Search in Going Medieval
This will then give top priority to healing wounds for that settler, but it will only work if that settler is in bed. So to force a colon to go to bed so they can be cured, you'll also need to set their recovery job as priority one. This will effectively force them to go to bed to be healed whenever they complete their current task.
Additionally, if your colonist is in critical condition, you can prioritize healing them by selecting another colonist and then prioritizing wound healing over the injured colonist.
For more on Going Medieval, check out How to Store Food in Going Medieval and How to Get More Settlers in Going Medieval
