DAE get back spasms when getting ur hair done?

I've experienced this since I was around 10. Whenever I get my hair washed, my back suddenly jerks, especially on the right side of my mid-back. It happens randomly and is quite uncomfortable. It's been a problem now, in cosmetology classes where we frequently wash each other's hair, and also during facials, the same thing occurs when they touch my forehead during a facial. Does anyone know what causes this and why it happens?