A unicold is similar to a human cold, except it only affects unicorns. It is a relatively common ailment in the winter, when ponies are confined in closer quarters in their homes.
A unicold starts off as a general feeling of malaise, weakness, irritability, and muscle soreness. It then progresses to a runny nose, sore throat and copious amounts of sneezing. These symptoms are the most common, and they usually last for about a week or so.
There are a few complications with the Unicold that go beyond the standard symptoms. These include the inability to control their magic, which can cause them to cast spells they don't know, or even their magic not working at all. The most severe symptoms involve the unicorn casting very advanced spells, well beyond their control, often with disastrous results.
There is no known cure for the Unicold, with the prescribed method of treatment being rest, drinking plenty of fluids, and completely refrain from using magic. Use of magic can, and usually does, worsen the symptoms and could lead to bringing on the more severe symptoms detailed above. A unicold will run its course in about a week's time, so just hang tight.