Random crash when opening a world

So I tried to open my world and, at first it said server closed, and it automatically went to the multiplayer servers screen, whereas I was at my worlds. Then, I tried again and it opened the world for 2-3 seconds, it was really laggy, not even a frame per second, and then it crashed. I don't know if it matters, but this happened right after closing the world in MCEdit. Just so you know, everything was done right. I saved it, then closed it in MCEdit and then opened the world via Minecraft, then it crashed.