What Causes Numbness Feeling Around The Neck?

Hai,I am 25 year old male.I am having a numbness feeling around the neck and also to back of head.also feeling that my concentration has dipped a little bit. This is started after i have wrongly practised yoga giving max strain to my head nerves wrongly. I have consulted a docter at that time. The MRI of my head and neck show no abnormalities. But the fact is that I am feeling this problem very heavily since 6 months. can i get an advice on this matter? Please help