Adrenaline/butterflies when trying to sleep.?

I am trying to get to sleep and just as I am about to drift off to sleep, I get this mild adrenaline rush, like butterflies in my stomach. I have never gotten this before and am perplexed.

I have done some cursory online investigation and the signs seem to point to a nocturnal panic attack. However, this seems to be linked to drug withdrawal and/or pre-existing chronic anxiety, neither of which apply to me.

I do have a possible cause for it, but it is purely psychological and not physiological in nature. But again, nothing I have yet found points to acute psychological issues causing this.

Does anyone out there have any answers?