Recurrent Patella Dislocation. Shower?

I am a Engineering Student, with very less physical activities and no involvement in any kind of sports. I also don't do any exercises regularly. I had two episodes of recurrent patella dislocation, one a month ago and another about 4-5 months ago ... That too without an injury, First episode occurred to me while I was just walking on the floor and fell down and then observed that patella got dislocated and popped back into the place automatically In Second episode, I was just taking the bath and fell down and observed the same. I didn't observed any swelling in the first episode and pain also stopped after few hours while there was some swelling and pain in the second episode which lasted for about 7-10 days. My doctor suggested me to have surgery, even without having MRI. Please suggest me what should I do in this case? Also, what should be the reason for having patella dislocation even without any injury or direct impact in the knee... While just walking or standing in shower ??