Sitting in recliner or laying in bed try a roll.
I roll a long bath towel, and put hair pony tails/or braid bands 6" from each end. Take roll, and use as Japanese do adjusting from curvature of neck moving up to back of head periodically as you find different pressure points. Stiffen and soften (by loosening or tightening for comfort) the roll. Do not follow me! Ask your doctor please.....Q

After seeing this picture, I'm thinking of buying a neck pillow (type you use on an airplane) for my hubby.

Do you have specific exercises from a physical therapist to help this? Check your sleeping position especially when you fall asleep sitting up. I try to always use a cervical pillow & sit very straight if I might doze off.