You're right, it is terrifying. I have experienced sleep paralysis several times over the years and have found a link between the frequency and stress in my life. I also believe there is a link between that and disturbed sleep (so it can be a bit of a vicious circle)
As this is the first time it has happened to you I think you could probably chalk it up to stress and anxiety. If it happens to you again a few more times, mention it to your GP (although to be honest my GP knows nothing about the subject, but you could keep asking until you find someone who does)
I'm sorry you're going through a tough time. I hope you're feeling stronger today.