There are number of medications that can cause sleep paralysis as well. Basically, anything that messes with your body’s serotonin levels has a chance of causing a sleep paralysis. Besides the prescription drugs that can cause this problem, users of Ecstasy may find themselves suffering from sleep paralysis after long term use. In addition, both prescription drugs and Ecstasy can cause waking nightmares. These are hallucinations that happen when you first wake up. They are usually connected with the sleep paralysis, such as a hallucination of someone sitting on your chest or pinning you down.