Hi, welcome to the forum, sleep paralysis
can be a manifestation of type of sleep
disorder like parasomnias.
Few of the individuals are known to suffer from parasomnias esp. when they are on non-benzodiazepine sedatives, drug abuse etc. otherwise no definitive cause exists in few individuals apart from stress, positive past history of abuse etc.
The associated symptoms with the following disorder are confusional wakefulness, sleep paralysis, nightmares and night terrors.