Usually a stiff neck is a result of stress or staying in a poor position for too long. There are available cervical pillows for resting on you might look for- Wal*MArt might have them. If the stiff sore neck is accompanied by a headache and fever-see your doctor. Otherwise- a chiropractor might be able to help.
I am not a doctor but I also have the problem you have. My left shoulder is always "in a knot". It is stress in my case. Maybe you need to see a doctor to rule out disease. It's probably not your heart. Good Luck!