Doctors have long known that folks with CP are more at risk for sleep problems. Children who have cerebral palsy have neurological problems that may contribute to seizures, and uneven motor development, both of which can affect the sleep cycle. As @Harp said above, sleep problems can ensue because of the discomfort while sleeping. Poor motor control can contribute to sleep apnea.
In addition, some people with CP have emotional or attachment problems because they need so much help in accomplishing daily tasks. Thus, if left alone to sleep they begin to worry and then cannot sleep.
Physical therapy can help with muscle pain. Medication can help with seizures. Light sedatives, melatonin, or anti-anxiety drugs can also be helpful.
You need to talk to your doctor about why you are having trouble sleeping. He/she can order sleep studies and prescribe treatments that can help.