Sudden appearance of veins on chest and upper arms they are large and dark blue are from upper arms to front of shoulders to chest and top of breast?

Venous obstruction: The veins could be collateral vessels that are prominent because of venous obstruction in the shoulder. This is most likely caused by a venous thrombosis and can be diagnosed with a venous ultrasound. Have that done asap. If you have a venous thrombosis, seek the help of a vascular surgeon.

Central stenosis: This could possibly be related to a stenosis (or narrowing) of the veins in the center of the chest or in the top of the arm. A vascular specialist could help diagnosis this with possibly an ultrasound or other imaging study.

Svc syndrome: Could be blockage of the main vein in the chest.