Trapped nerves in your neck giving pain into your arm and/or hand. Nerves which run from your neck to your arm can sometimes get irritated or compressed.
There are different reason why they get trapped from muscle tension to discs in your neck pressing on them. The pain can be severe sometimes so get advice from your GP or pharmacist to help control the initial pain. Other symptoms might include pin and needles, burning or weakness of your arm or grip.
An osteopath is well trained to help you with this kind of problem and can get you on the road to recovery. You might also benefit from massage and acupuncture after the diagnosis is made.