Left arm feels weak/heavy when i sit or lie down in certain posture. neck will feel choked sometimes. start to have shortness of breath. what is this?

Neck: It's possible that you have an impingement of a nerve or nerve root from a disk or spur in the vertebral area of the neck. This shouldn't impact your breathing however. This shortness of breath, especially if it's only at rest, may be from anxiety. A neurologist is best qualified to evaluate the neck, arm symptoms and order appropriate tests or refer you to another specialist.