@Elvira81 Do you feel vibration around your heart when you lie down and does this vibration go away if you lift your back off the bed ? Do you feel any tightness or skipping of a heart beat when you climb down a staircase ? The intestines are so arranged that the stomach bag sits on top of the large intestine's transverse part (Transverse colon) The large intestine is so arranged that the ascending colon, transverse colon and descending colon engulf the small intestines (which is like a ball of noodles).
The purpose of the stomach bag to sit on the transverse colon is that as soon as you wake up in the morning and have a cup of coffee or breakfast the food lands in the stomach bag and it exerts pressure on the transverse colon. This is called gastro colic response. As soon as pressure is exerted the intestines release serotonin and a major contraction (peristalsis) is initiated and bowel movements happen. This process is very finely coordinated between the brain and the gut with the spinal cord acting as the carrier of messages between the two.
If the intestines go rigid (both large and small) this mechanism goes haywire and you start feeling pressure in your chest and abdomen cavity. I used to feel a tightness at the back of my neck. It caused vertigo like symptoms. This is because the balance nerve goes through the neck.
So I used to get palpitations after breakfast and it used to subside on defeacation. The symptoms can vary vastly from person to person. Once the motility and peristalsis is increased the system sets itself right. So please consult a gastroenterologist (Physician). Hopefully this symptom should resolve. I dont know what your energy levels are. If you can do gentle exercise like yoga for cfs or walking for 15 min. you can ensure that it does not repeat.