What is your diagnoses
This is not sinus arrhythmia, more like sinus tachycardia. Every QRS has a p-wave, and are narrow complex, with a regular rate/rhythm. Sinus tachycardia in a 20 yr old can indicate a congenital problem, I.e. WPW(Wolff Parkinson White), etc, drug/stimulant use, infection, or other causes. Examine patients history, as well as blood work to determine cause. But by itself, sinus tach is less likely to cause other issues than atrial fibrillation.