The situation:
You are a doctor. There are two new diseases in the world. They aren't transmitted by contact with an infected person, and it is unknown how you get them. They both have the same symptoms. These are: tiredness, short attention span, blurred vision and ringing in ears. They are equally common - there is absolutely no way of telling the difference between them. However, they each have a very different cure. If you give them the wrong medicine, it makes the disease worse - they become very tired, but are unable to sleep, they go completely deaf and can't see clearly any further away than about a foot in front of them (glasses etc don't work). If you give them the right medicine, they are completely cured, immune to both forms of the disease AND all other diseases.
The choice:
In your clinic is a patient with one of the diseases. Do you attempt to cure him/her?