1-Menopause must have
2- Cervical injury, surgery ,  degenerative disc disease...you name it ,i got it or had it wrong with my neck. I did go to a local furniture store to try each size available before I ordered. Loved it since first night using it. Only con is it doesn't stay as cool as I'd like but it does stay mildly cool. I sleep on my back and both sides. I'm 5'5" wt 185. God bless