then it is probably about your relaxation , within your breathing.

I found out for myself since i had the same problem 2 years ago. i got everything paralyzed except my upper body(stomach up).

Learn how to breathe. sounds stupid, but helps a lot.

best way to do is actually mimic your sleeping breath, to do that you need to record it first, up to you how you do this, but probably the best way is to let somebody else sneak into your room and record it or just set up a mobile phone and let it record 3 hours , set alarm clock. And train yourself the breathing via meditation listen to it, mimic it, feel the calm state, and when you re attempt WILD, get into this state, and voi la