I have successfully treated narcolepsy (take provigil, xyrem). About a year ago, I suddenly developed severe chronic insomnia. What could cause this?

Insomnia. Check the time and amount of Provigil that you take identify other stressors try Ambien (zolpidem) short term or increase xyrem also cbti has good results.
Have you had a . Comprehensive sleep medicine evaluation with polysomnogram since this change in sleep? If not, doing so may provide the information you seek. Take care.