It could very well be related to the vagus nerve. Entanglement of the vagus nerve causes hiatal hernia (there is a hernia forum here). Why do think "adrenals", any problem with them during the day? Don't drink diet soda, Aspertame deteriorates the myelin sheath in the brain and also causes heart palpitations.
It might just be a simple digestive cure (don't panic and imagine anything serious). Sea Salt is good for sleep and many other things.