It is probably just a positioning thing as you have stated. It is likely that you have an extra rib, known as a cervical rib, or more developed neck muscles, leading to blood flow obstruction in the jugular vein when you raise your arm causing these findings. Having the cervical rib or larger neck muscles is a normal variant. I wouldn't worry about the neck vein distention, epsecially if it is an isolated finding in you. Patients who have heart or liver disease have other findings of those syndromes such distention and swelling in the abdomen and the lower extremities, skin changes, shortness of breath with exertion or during sleep, fatigue, etc.
Thank you so much for answering me so quick! I feel much better about it!
I have the same thing but has progressively worsened.. No one knows what to do yet either! Now I beleive it is heart connected.