UE4.15.1 Randomly removes place FBX files

While working in unreal engine 4 placing objects itc, its randomply without any warnings deletes half of my progress most of my shaders and a random assortment of objects. leaving me with the message in the attachment

. please help!
I will also mention, nothing has changed at any point, i have not moved ANY files i have not deleted ANY files i have not done a single thing other than press save every five minutes. I think this crash happened when i was importing assets, BUT the crash before it happened as i was saving. So its different every time.
I really don’t want to start again this is a degree project that is due in a week. And it was basically finished before this all started.
please help

OOH also, quick aside here, would filling up your drive as i work be the caise? as i think that happened as i was working it got fulll but would that cause these weird pathway glitches?