Fell of a horse today and i have really hurt my neck...cont?

basically she was excited and did a massive jump and PLOP i went onto the floor...i wasn't hurt at the time, apart from felling a little sore or my right side where i landed...my neck is hurting on the left, and im not sure what to do, its like a constant pain that is there and when i move (particually to the left) it becomes worse...what do you guys think i should do/what it could be, thank you xx