What happened to my bike?

[Ripper0428]

I have a 26" mountain bike that I was riding the other day. I stopped at an intersection for about 30 seconds and when I went to start again the rear wheel popped off. When I look at the hub/axle area it appears that the axle has lengthened and possibly shifted position in the hub. Does anyone know what happened and what I can do to fix it, or should I just take it to the shop.

[cyclerUK]

Possibly the axle has snapped?
Or the the fixing nut has come loose.
Check the tightness of the nuts and then get hold of the wheel and see if it wobbles.
If the axle has snapped then part of it should pull out when the wheel is removed.