Sounds like you have Sleep Paralysis, I have Sleep Paralysis and the same thing happens to me. Good news is it's not deadly, You will always wake up from it. You can talk to your doctor about it too.
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. This can occur in any sleep stage (REM and non-REM stage).
To rule out parasomnias you need to undergo Polysomnyography and sleep analysis. You need to take out time for further evaluation. Short term benzodiazepine against prescription will help you. Most of the time it is temporary, it will disappear over a time. There is nothing to panic. I suggest you to consult physician or sleep specialist. Take care and regards.