I was at work and walking and all of a sudden I fell? I had this happen once before the doctor couldn't find out why.

Go to symptom checker dot com. :) See if you have any more symptoms to put in.

Did your knee lock up? How did you fall??

Did you fall or did you collapse? There's a huge difference...

If your knee didn't lock up or give out, did you slip on something? Did you pass out? or faint??

this has happened to my father a couple of times.he has had blood tests and a MRI and a cat scan and nothing.my hot neighbor is a dr at VA hospital in boston and i told him what was going on.because my dad also suddenly hunches over.he said something about his top 5 vertibre.but he keeps falling.i think there is something wrong i dont care what the drs say...

So for awhile my leg kept giving out, and I went to see my doctor about it (it was accompanied by lower back pain too though) and they did some MRI's and found out that I had 2 bulging disc's, and 1 that was herniated. The bulging ones were pressing on some nerves and also causing my actual spinal column to narrow, and causing all sorts of problems.

Dunno if t his helps, but my mom had a problem with what she thought was her hip going out and it would cause her to fall. When she finally found someone who knew what they were doing, they found out that she was having problems with her sciatic nerve. It took going to a chiropractor and getting her entire spine and stuff realigned before the problems subsided.