Welcome to HCM! I have gone through your question carefully and from my clinical experince I can say that your presentation is due to some kind of vascular problem, possibly related to inferior vena cava compression. I can say this because there is significant swelling of veins in neck and upper half of body when tummy is pressed. You have not mentioned if you suffer from many kind of vascular problem, like: arthreosclerosis, etc. as this also can be one of the causes. There is difficulty in breathing when there is compression in abdominal area, also points to venous congestion in lungs....related to blockage of blood vessels. If you are hypertensive, ( though not mentioned in question), then I must say that you need to revise your medicines, as the problem can increase with uncontrolled blood pressure. You should meet a doctor, preffrably physician, get your blood pressure checked, both in upper limbs ( in sitting and lying down position) and lower limbs and pulse of all four limbs. The doctor may go for some test to check the flow in your major blood vessels. Till then, please stop smoking and alcohol altogether (if you consume them.) Please see the doctor, as no medicine can be given without examination and finding exact cause. Hope the reply is useful feel free to ask more questions Dr. Manisha Gopal