Greetings Madam. First of all i appreciate you for giving importance(to small changes happening inside self) for health. My opinion is that you should not worry about it now unless there is associated pain in left sided chest (feels like squeezing type/ heavy weight over chest etc.,)with pain radiating to shoulder-jaw-left arm; breathing difficulty, increased sweating with rapid heart rate. As per your details given such as 1. Age-Height-Weight - It s normal for your age. 2. heartbeat skip - chest goes up in neck & then goes down in Stomach(is a Normal Respiratory pattern of individual ) - blackouts when getting up( from sitting & lying down)- occasional chills with Goose bumps- Everything is normal physiological routine things happening in all human beings with or without their knowledge. But the thing which i could not interpret was Breath hard to take in Today which was frequent and bad feel . Otherwise you seem to be normal. I suggest you to wait atleast 2 days and divert your mind to your routine work/ reading Books/etc., instead of thinking about that movement sensation. Even after doing the above said if that lastly said HARD FEEL SENSATION not getting relieved or becoming worse than before, It is advised to consult your nearby General physician once for complete examination n further management.