Why do people do this - [she] just stopped calling?

I recently started hanging out with this girl who I have known for several years; we had our thing in the past (nothing serious), and it just so happened right now was a good time for us to connect again. We had an amazingly fun week last week doing all sorts of stuff. Everything was going great, until yesterday when she just dropped it like bad habit. No call, no txt, just fell off the face of the earth. Literally her last text to me was asking if she could come over to hang out before she went to work.

Both of us have gotten out of pretty serious relationships about 5 months ago; that might be a factor, but perhaps there is residual drama.

Either way, I’m sure the reason could be anything, but I guess I just want to get my fluther community opinion. Have you done that to someone – just stopped talking, no call no show on them? if so why?