Tachycardia, or a high heart rate, is defined as a heart rate above 100 heartbeats a minute. Tachycardia can be a normal response to physical or mental stress. In all other cases (heart disorders, for example) tachycardia is not normal. Tachycardia can be with a normal rhythm (such as during sinus tachycardia) or can manifest as an irregular rhythm (tachyarrhythmia). According to your description, it seems that you are experiencing tachyarrhythmia.

Therapy of any tachycardia depends upon its cause. The cause for an irregularity can be outside the heart (anemia, hyperthyroidism, tumor that produces adrenalin, febrile conditions, lung disorders, physical efforts, anxiety etc) or can be located inside the heart. Postural orthostatic tachycardia syndrome (POTS) is a condition of orthostatic intolerance in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, often, but not always accompanied by a fall in blood pressure. POTS is due to a disturbed reflex that controls the heart rate.

You didn’t tell me what is your heart rate while laying down. You also didn’t tell me if you've performed any laboratory tests (thyroxin, adrenalin, noradrenalin, blood count, hemoglobin etc.). You can consult a cardiologist about your condition to request these diagnostics and have a specialist take a look at the condition. If tachycardia disables you from working normally, you may need to take medication.

POTS - Postural orthostatic tachycardia syndrome - can I cope w/o medication?