Hi welcome to the health care magic It is difficult to predict exact cause without examination but it could be acid reflux induce chest pain as happen in lying down position ... If acid reflux and acidity history present than omeprazole prescribed for that Your work up done as follow... -Auscultation -x ray chest -EKG According to cause specific treatment given If no specific cause found (including abdominal causes ) than muscular pain might be the reason Hence with keeping these in mind consult nearby physician or pulmonologoist for examination and further work up accordingly Take care