Thank you for your question.
Sometimes your sitting posture can increase you intra abdominal pressure . This can cause upward pressure on your diaphragm , displacing your heart forward, it may also irritate the Vagus nerve
that supplies your stomach and heart. This can elicit your symptoms, these are not dangerous and should not last for long. If this keeps reoccurring please consult a doctor to examine you.
I trust this will put your mind at ease.