<s>[INST] Hello, i am 20yrs. old and when night fall comes around my heart begins to beat very rapidly causing shortness in breath, dry mouth, sometimes it feels as is my heart is going to pound out of my chest. However, during the day i am fine its only past 8 or 9pm [/INST] Hello, Your symptoms could be related to anxiety. At your age, it is less likely to suffer from any cardiac disorders. Anyway, if the problem persists, I recommend consulting with your attending physician for a careful physical exam and some tests: - A resting ECG and cardiac ultrasound- A chest x-ray study and pulmonary function tests to exclude a lung disorder- An ambulatory 24-48 hours ECG monitoring to examine your heart rhythm trends during the night-Complete blood count for anemia-Blood electrolytes for any imbalance-Thyroid hormone levels for thyroid gland dysfunction. You should discuss with your doctor on the above tests.  Hope I have answered your query. Let me know if I can assist you further.  </s>