<s>[INST] I am an 18 year old girl without any known heart problems. I woke up very early this morning with a tight chest and a little bit of pain. It worried me a lot, so I didnt get much sleep. It feels better than it did, unless I have my heavy bookbag on my back. [/INST] Thanks for your question on Chat Doctor. I can understand your situation and problem. In my opinion you are having mostly muscular pain. But better to rule out cardiac cause first. So get done ECG. If ECG is normal then no need to worry much for cardiac cause. You have improved with weight on chest, this suggests muscular pain more. So avoid strenuous exercise. Avoid heavyweight lifting. Avoid bad posture and movements in sleep. Start painkiller and muscle relaxant. Apply warm water pad on affected site. Don't worry, you will be alright. </s>