This sounds like a grave problem and one that should absolutely not be ignored. Please see a doctor as soon as possible in order to determine the exact nature of your injury. Such a high jump also comes with a lot of pressure applied to the area that hit the injured spot and general area, and the injury may very well be deeper and more complex than what appears on the face of it. Only a doctor can tell if you need to go for further diagnostics such as an x-ray or a MRI which will tell the exact nature of the injury. If the doctor gives a clean bill of health on this one, then there can be some easy measures that can be taken to provide relief and comfort. However the best kind of solution for this sort of an aggravated injury is rest. If possible, please take complete rest for a few days. This alone will be helpful in getting the impact of the injury down to a great degree. The best posture for the neck if it has been injured is to lie flat without a pillow. Not only is this ergonomical for the spine, it is also the best way to provide complete rest to an aggravation caused by an injury.
Application of warm compresses is useful in helping to bring down the inflammation and will also provide soothing comfort. If this does not work for you, as it does not for a lot of people, then you can just as easily switch to cold compresses. This will be useful in helping to bring down the inflammation as well. The kind of compress you end up using depends on what type of an injury this may be. The one thing you would need to guard against is massage. While this may feel good at a purely superficial level, this can have far reaching and damaging effects in the long run. While pressing down on the body during a massage, there is absolutely no way of knowing what can work for or against the body. So, simple applications without pressure of any kind usually are the best way to go. Please do keep in mind that it is not always possible or feasible for the doctor to gauge what kind of an injury this may be. If you find that there is no change in the state of your neck after a week of trying to rest and allow it to heal naturally, or that the pain or discomfort has worsened, please have yourself checked by your doctor.