Orgasm with no arousal?


I cant get aroused anymore be it myself or with my partner and havent been able to for about 4 years. Strange thing though is that if i masturbate like i used to i can still acheive an orgasm but with no arousal. I know for sure that it is an orgasm as ive had them before, the doctor said that this was impossible? Any suggestions of how to get my arousal back? Thanks