Usage depleted overnight. All updates set during free time.

Sat down to check data usage at 1:30, meter said 85%.  I turned wifi off on my phone ( I'm testing everything) it had been on all day.  Within 30 seconds my meter dropped to 52%.  and within the next few minutes to 47%.  I walked away for about 10 minutes, came back to 45%.  I know that I did not use that much data!