I have this tightness on the chest and shortness of breath when I'm laying down trying to take a nap.?

Unsure. Your symptoms occurring at rest are concerning. You should be examined by a healthcare professional to make sure it is not heart related.
Orthopnea. This sounds like orthopnea; it suggests a possible problem with your heart. Unless you are pregnant, it would be a good idea to go see your doctor about this to run some tests. If you are pregnant, then this can actually be normal later in the pregnancy, as the weight of the baby pushes up on the diaphragm and makes it harder to breath. Heartburn can sometimes present this way too. Goto doctor!