Compo Syndrome is caused by excessive compoing.
Compo Syndrome symptoms usually appear gradually as one starts compoing more. Common symptoms include not knowing how to to pick samples or synthesizer patches, not spending longer than an hour on non-OHC songs, and frequently demanding that a compo be held. In the most severe stages, a person with Compo Syndrome is unable to produce any music outside of a one-hour compo.
Currently, the only known cure is to force oneself to make music outside of a compo.