Lost a lot disk space while playing UT?

I been playing UT 2015 and i updated the game and before starting the game i had 16,5gb free on my HDD and i enjoyed playing and suddenly the game crashed and i did ctrl alt delete and game was showing not respoding status but what is even more weird i noticed that on my disk space only 13mb were left?how can suddenly in about half hour 16,5gb disappear without any download or similar at that time?I restarted the notebook and windows didnt updated so that isnt neither.Can someone explain me how is this possible?i will try to recover the disk space by defragmenting cause cc cleaner gave me few MB just

 

sounds like the notorious 'full disk' on Windows 8/8.1? I've not experienced it since I've just installed windows 8.1 on my machine but have heard a lot of people having that problem. Hope this link helps:

http://www.instructables.com/id/How-to-fix-100-disk-usage-for-Windows-81/

 

Thanks for reply i will give a try after defragmenting finishes.Im on windows 7 x64 still until first dx12 games come and patches
Will update tommorow if it was solved.Hope others have some suggestions also

 

Seems my system recovered half of the size.Im on 8gb now but defragmenting didnt do nothing.It just recovers alone after some time.Weird but i expect in a day or two to have again about 16gb.I just thought some of you guys know the reason for such a loss in disk space