Hey there, try taking something for pain, whatever you use and resting on a heating pad for awhile. It could do wonders for the neck.
I have a tendency to have a lot of stress in my neck and upper shoulders and I use heat and Ibuprofen which usually takes the kinks out.
Good luck at your Doctors appointment.
Don't try to over think this as you may have just pulled a muscle or laid on one side that caused the pain to be on one side.
Have you tried the heating pad and NSAID meds?