It has happened me 3 times, once a few months ago and twice in the last week. I start the car and I thought it was stalling when I was going from 1st to 2nd gear but the last time I revved the car before moving and it seemed to lose power after 2000rpm and shudder to a halt. The previous 2 times I pressed the starter button a few times and it wouldn't start, and then a after a few attempts it would get a bit off life and then it would start, after which the car would seem perfectly fine. The latest time, however, it would not restart at all. There has never been any engine management lights, and you coincidentally on the day it happened let I had brought it to a mechanic and his diagnostic computer showed up no faults. I had previously taken it to another mechanic and he had no clue what it could be. Would really appreciate some help!

 

Take it to Mazda.