As per ypur history, if it was a single time episode- nothing to ne worried of (as you already ruled out head ache/ other neurological symptoms)
It is probably Sleep paralysis - which we see in REM Sleep, where your body is relaxed but your mind works as if u are awake.
Nothing to be worried of if it doesnot frequently occur
Usual triggers are stress and orregular sleep patterns
Next Steps
You can contact me via practo video consultation for further discussion