<s>[INST] Hi, I am 29yrs old, had difficulties a few weeks ago where I passed out cold twice in the space of 30mins and have been feeling very tired and light headed since. My doctor did blood/urine tests which resulted with no problems. He is now having me do an ECG today which I am a little concerned about! Is it just routine? I am usually VERY energitic and so this feeling and obviously losing consciousness has been worrying me a lot. [/INST] Hello and welcome to Ask a Doctor service. I have reviewed your query and here is my advice. Most likely you are having cardiac arrhythmia like supraventricular tachycardia. It's basically abnormalities in heart rate where rate is very fast and BP Chat Doctor.  It's possible that your would be normal because it can pick only during episodes. You may extend holder monitoring, which is the device which monitor ECG and exactly diagnose the arrhythmia. If episode doesn't recur then it may not pick the arrhythmia. Last and best option is electrophysiologist studies which will diagnose and treat arrhythmia permanently in most cases. So you need to visit cardiologist as early as possible. Also, if you are getting the feeling of having episode then you should try to cough hard to abort the episodes. Hope I have answered your query. Let me know if I can assist you further. </s>