Why do I collapse then?

So if I have L4 L5 prolapsed disc,which my MRI said i have, would this make me collapse, I just give way without warning really, this bothers me more than the pain but wondered if it was the prolapsed disc that is doing this?:(

It can do. Most often people collapse because of a sharp pain rather than a loss of strength... but a significant prolapse that compressed the nerves could cause you to collapse. But thats quite a significant prolapse - the doctors would probably be looking to do surgery in that case.
It doesn't mean that it is though! There are hundreds of other reasons for collapse - talk to doctors re: blood tests etc to screen for other possible issues.

thanks -it doesnt hurt when it happens, other than landing on the floor(!) I am awaiting an MRI and surgery was mentioned, but hoping to find a miracle working physio in the midlands to avoid this!! cheers.:o

what are the caused why some people tried being collapse?

ryxin01 - there are too many causes and also different types. If one falls because of blacking out briefly then it is syncope and there are many medical reasons. If you don't black out then there are still many others, the most obvious being poor balance - and there are many many causes for that from pharmacological to systemic issues.