Answer:
you can be anemic, or have drank coffee, worse case scenario you could have underlying disease, be obese, have diabetes, you may have taken some strong medicines such as vitamins (vitamin D, Iron) you may have covid (but shortness of breath and rapid heart beat is only one symptom of covid) you could be anxious and have anxiety or any other mental health disorder, you may have acid reflux (when you sleep or lay down you have a gassy stomach or you cannot breathe well)
Step-by-step explanation:
if you do have heart palpitations and shortness of breath, take a slow walk, drink green or herbal tea (non caffeinated) , sleep with your head elevated, get some fresh air, if condition persists and feeling pain in heart (on left side of your chest) go to hospital.